Article

Cultural eutrophication in the Choptank and Patuxent estuaries of Chesapeake Bay

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Abstract

The Choptank and Patuxent tributaries of Chesapeake Bay have become eutrophic over the last 50-100 years. Systematic monitoring of nutrient inputs began in ;1970, and there have been 2-5-fold increases in nitrogen (N) and phosphorus (P) inputs during 1970-2004 due to sewage discharges, fertilizer applications, atmospheric depo- sition, and changes in land use. Hydrochemical modeling and land-use yield coefficients suggest that current input rates are 4-20 times higher for N and P than under forested conditions existing 350 yr ago. Sewage is a major cause of increased nutrients in the Patuxent; agricultural inputs dominate in the Choptank. These loading increases have caused three major water-quality problems: (1) increased nutrients, phytoplankton, and turbidity; (2) decreased submerged grasses due to higher turbidity and epiphyton shading; and (3) bottom-water hypoxia due to respiration of excess organic matter. Oxygen in the Patuxent is consistently , 3m g L 21 in bottom waters in summer, whereas oxygen in Choptank bottom waters has been decreasing for the last 20 yr and is now approaching 3 mg L 21 in wet years. The low N : P of sewage inputs to the Patuxent results in an N-limited, P-saturated system, whereas the Choptank is primarily limited by N, but with P limitation of phytoplankton during spring river flows. Insufficient action has been taken to improve the water and habitat quality of these estuaries, although reduced eutrophication in dry years suggests that both estuaries will respond to significant decreases in nutrients.

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... The lower tidal river also experienced a decline in nutrient concentrations; however, the effects on phytoplankton concentrations were minimal. 13,14,15,16 The relative importance of P and N as the primary culprit for stimulating poor water quality and habitat conditions can vary regionally. In the case of the upper tidal Patuxent River, after sustained reductions in P, additional reductions in N were necessary for sufficient water quality improvement to support the reestablishment of SAV. ...
... Over the past 20 years however, wastewater flows in Easton have slowly increased due to an expanding population and associated urban development, counteracting the benefits of WWTP upgrades. 14,58,59 Construction of BNR and enhanced nutrient removal (ENR) was completed in 2007, resulting in additional load reductions. The largest WWTP in the basin services Cambridge, MD, at which BNR and ENR were implemented in 2003 and 2012, respectively ( Figure 5.2). ...
... 14,59 Wheat and corn yields have increased over the past century, likely in part due to increased fertilizer use and new genetic strains of plants. 14 The water quality monitoring station in upper Choptank River near Greensboro, MD has revealed continuing increases in TN and TP concentrations ( Figure 5.4). 59 Additional factors may complicate system dynamics, such as the import of P from the Chesapeake Bay into the Choptank River. ...
... Streams draining human-altered landscapes are at risk for poor water quality due to anthropogenic contaminants (e.g., Norvell et al. 1979;Novotny et al. 1985;Jordan et al. 1997a, b;Fisher et al. 2006;Powers et al. 2016). These contaminants include nitrogen (N), phosphorus (P), and total suspended solids (TSS), which can impair not only stream systems but also contribute to accelerated eutrophication and impaired ecosystem functioning in downstream receiving waters (e.g., NAS 2000; GOM Watershed Nutrient Task Force 2001; Kemp et al. 2005;Fisher et al. 2010). ...
... In agricultural regions, the primary sources of contaminants are animal husbandry and surface applications of fertilizer and manure for crop production (e.g., Correll et al. 1995;Denver et al. 2004;Beckert et al. 2011). These activities contribute anthropogenic N and P to the soil which leaches into ground and surface waters (e.g., Correll et al. 1995;Pionke et al. 1996;Jordan et al. 1997c;Fisher et al. 2006). During storms TSS is eroded from organic litter and mineral particles in the upper soil layer, as well as from stream bank erosion and re-suspended bedload from the bottom of the stream channel (Kuhnle et al. 1996;Thompson 2008). ...
... The volume and chemistry of baseflow varies primarily over time scales of weeks to months (e.g., Fisher et al. 1998;Sutton et al. 2009;Vanni et al. 2001). In contrast, stormflow consists primarily of overland flow from the stream's contributing area during wet weather, and the volume and chemistry of stormflow vary over shorter time scales of minutes to hours due to rapid fluctuations in precipitation and overland flow (e.g., Correll et al. 1999;Fisher et al. 2006). While lasting only for brief periods, storm events can have a disproportionately large effect on seasonal or annual nutrient and sediment export due to high concentrations of N, P, and TSS and large discharge volumes that occur during storm events (e.g., Correll et al. 1999;Pionke et al. 2000;Gonzalez-Hidalgo et al. 2013). ...
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Stream discharge and chemistry (total suspended solids TSS, nitrogen N, and phosphorus P) were monitored for 15 months in six agricultural watersheds on the U.S. Mid-Atlantic coastal plain. Watersheds with similar land uses and a range of hydric soils were used to test the hypothesis that hydric soils generate large storm discharges due to low permeability, resulting in watershed areas with high loss rates of N, P, and TSS. To test the hypothesis, discharge was monitored continuously, and a flow separation method quantified the base and stormflow contributions. Another primary goal was to measure base and stormflow chemistry to quantify N, P, and TSS export. Baseflow chemistry was monitored monthly, and 31 storm events were sampled. Baseflow chemistry varied little over the 15 months, but stormflow chemistry was dynamic, with three major patterns: (1) TSS and particulate N and P had large, brief peaks during the rising limb of storm hydrographs; (2) phosphate and ammonium had broader peaks close to maximum discharges; and (3) nitrate concentrations decreased during the rising limb, slowly returning to pre-storm levels. Event water yields were correlated with volume-weighted mean concentrations (VWMs) of N, P, and TSS, providing a basis for estimating VWMs of unsampled events. Export coefficients (kg ha⁻¹ year⁻¹) ranged over 22–33 for TN, 0.9–1.4 for TP, and 240–1140 for TSS. Most P and TSS export occurred during storms (71–99%), while most N export occurred during baseflow (52–84%). The discharge data did not support the hypothesis, and watershed slope, not hydric soils, was the major control on storm discharge. Surface ponding of water on hydric soils intercepted runoff, reducing the impacts of the low infiltration rates.
... The majority of freshwater flow (64%) and nutrient-loading of Chesapeake Bay is from the Susquehanna River (Boynton et al. 1995, Kemp et al. 2005, while there are several major tributaries on both sides of the Chesapeake Bay, including the Patuxent River, Potomac River, Rappahannock River and Choptank River. Extensive studies of nutrient loading and its processing by primary producers have been conducted on the Chesapeake Bay ecosystem (Fisher et al. 1990, Boynton et al. 1995, Cornwell et al. 1996, Malone et al. 1996, Harding and Perry 1997, Fisher et al. 2006. Massive terrestrial loading results in excessive phytoplankton production in the Chesapeake Bay (Malone et al. 1988, Malone et al. 1996, Adolf et al. 2006c, Fisher et al. 2006. ...
... Extensive studies of nutrient loading and its processing by primary producers have been conducted on the Chesapeake Bay ecosystem (Fisher et al. 1990, Boynton et al. 1995, Cornwell et al. 1996, Malone et al. 1996, Harding and Perry 1997, Fisher et al. 2006. Massive terrestrial loading results in excessive phytoplankton production in the Chesapeake Bay (Malone et al. 1988, Malone et al. 1996, Adolf et al. 2006c, Fisher et al. 2006. Generally, the peak biomass of Chesapeake Bay occurs during the spring diatom blooms, while peak production occurs in the summer when summer temperature reaches its maximum (Malone et al. 1988, Malone et al. 1996, Harding et al. 2002. ...
... The Chesapeake Bay region has been subject to eutrophication which is linked to the pressures of increasing human population, urbanization (e.g. Washington DC, Baltimore area), development of animal and plant agriculture and non-point nutrient pollution in its watershed , Hagy et al. 2004, Kemp et al. 2005, Fisher et al. 2006. As a consequence of this eutrophication, Chesapeake Bay has suffered from major harmful algal bloom problems for decades , Marshall et al. 2004, Tango and Butler 2008. ...
... The nitrate/nitrite concentrations of Capisic Brook are also the highest which is consistent with what is expected of urban watersheds. Royal River nitrate concentrations are slightly higher than expected for a mostly forested watershed, but the presence of agriculture and urban areas likely raises the nitrate concentrations (Boyer 2002;Fisher et al. 2006). The predominately forested Presumpscot River had the lowest nitrate concentrations (0.035 mg NO3-N L -1 ). ...
... Nitrogen concentrations found in the rivers that drain to Casco Bay are low. Concentrations found in rivers that drain to Chesapeake Bay (a more southern but still temperate estuary) are 1.5 -4 1.5 mg TN L -1 (Fisher et al 2006), whereas concentrations found in similar rivers in New England are lower. For context, total nitrogen concentrations found in the Choptank River, an agriculture dominated watershed (58% agriculture, 33% forested and 9 % urban) that drains to the Chesapeake Bay, averages around 1.5 mg TN L -1 (Fisher 2010;McCarty et al. 2008). ...
... Beaulac (1982) and Reckhow et. al (1980) compiled nitrogen export coefficients for agricultural, forest and urban landscapes providing a quantitative gauge of the anthropogenic influence from non-point sources within the watershed (Fisher et al. 2006). Comparing the nitrogen export coefficients of the three rivers in this study to values outlined by Beaulac (1982) and Reckhow et. ...
Article
Over the past two decades, total nitrogen (TN) concentrations have increased in Casco Bay (CBEP 2015). The sources of the increased nitrogen are poorly understood but occur with simultaneous population growth and land use changes. The total riverine nitrogen load to Casco Bay was previously estimated by Liebman and Milstead (2012) using the United States Geologic Survey’s (USGS) SPAtially Referenced Regression On Watershed attributes (SPARROW) model. The SPARROW model uses watershed characteristics, regional monitoring data and nitrogen source data to estimate nitrogen loading but was not validated using measurements of nitrogen in the Casco Bay watershed. This study attempts to estimate the nitrogen load from three rivers (Presumpscot, Royal and Capisic Brook), that together account for 78% of Casco Bay’s watershed (87% of the freshwater flow) and generally represent two distinct types of sub basins in the larger watershed (i.e., forested and urban) (Liebman and Milstead 2012). The TN loading estimates from the three rivers were then extrapolated to provide an estimate for the total riverine load to Casco Bay and compared to the previously modeled TN load estimates. Additionally, the riverine TN load was compared to other known TN loads from the other major sources such as atmospheric deposition, combined sewage outfalls (CSO) and waste water treatment facility (WWTF) effluent. Loading estimates for the three rivers were based on discharge and nitrogen concentration data from June 2017 – May 2018. We used Presumpscot River discharge from USGS gauge 01064118 near Westbook, Maine. Discharge for the Royal River was estimated using a historic watershed yield relationship with the nearby Sheepscot River which is still gauged. Capisic Brook discharge was estimated using the USGS Streamstats model. Water samples were collected at least monthly with an attempt to collect at both high and low flows. Water samples were analyzed for TN, Nitrate/Nitrite, and Ammonium. Water samples were not collected from December – March; concentrations for that time period are based on a discharge-concentration relationship, if present, or are assumed to be the average concentration of all data. Collectively, the rivers in this study load less TN than is discharged by the area’s five largest WWTFs. Presumpscot River, while loading the greatest total mass of nitrogen (173 Mg N yr-1), loads the least per hectare (1.16 kg ha-1). Capisic Brook loads the most total nitrogen per hectare (7.71 kg N ha-1) and Royal River loads more nitrogen than Presumpscot but less than Capisic (3.79 kg N ha-1). Land use is correlated with the mass of nitrogen per hectare exported via the rivers. For example, Capisic Brook has the greatest percentage of developed land use types followed by Royal then Presumpscot. For comparison, if we assume the WWTF’s discharge to their permit limit, the total nitrogen load from these three rivers accounts for less than half of the total nitrogen mass discharged into Casco Bay from WWTFs (902 Mg N yr-1). This study’s findings suggest that while non-point loading from river systems in Casco Bay contribute to the nitrogen content in the bay, they load less nitrogen than the areas of WWTFs. The amount of developed and agricultural land is correlated with the amount of nitrogen delivered to the bay by a river, which means that population growth will increase diffuse and point source loading in the future. And finally, this study’s estimates are in fair agreement with SPARROW’s TN loading estimate. More specifically, all estimates are within the same order of magnitude, but SPARROW’s estimates are a factor of two greater for the Presumpscot River and Capisic Brook. This study represents an important first step in understanding nitrogen loading to Maine’s most populous watershed and can be used to prioritize management of the largest nitrogen sources.
... . In the mainstem Chesapeake, algal blooms are common in surface waters (Glibert et al. 1995;Harding and Perry 1997;Sellner and Fonda-Umani 1999), and oxygen is depleted in bottom waters in summer (Officer et al. 1984;Hagy et al. 2004). The Choptank Estuary is currently undergoing the same degradation (Fisher et al. 2006b) that is now routinely observed in Chesapeake Bay. ...
... In contrast, the chlorophyll-a maximum in the Choptank occurs in shallower water (5 to 15 m), with weaker stratification and less isolation of bottom waters (Berndt 1999). As a result, there is less oxygen depletion in the Choptank despite higher annual average chlorophyll-a concentrations of 15 to 20 µg L -1 at the chlorophyll-a maximum in the water body (Fisher et al. 2006b), compared to 10-15 µg L -1 in the upper Chesapeake (Harding and Perry 1997). The dinoflagellate blooms known as mahogany tides that commonly occur in the Chesapeake Bay mainstem (Glibert et al. 2001;Tango et al. 2002;Marshall et al. 2004) are still only an occasional occurrence in the Choptank Estuary. ...
... The dinoflagellate blooms known as mahogany tides that commonly occur in the Chesapeake Bay mainstem (Glibert et al. 2001;Tango et al. 2002;Marshall et al. 2004) are still only an occasional occurrence in the Choptank Estuary. Despite the somewhat higher average chlorophyll in the Choptank, the shallower bathymetry and weaker stratification has limited hypoxia in bottom waters, although it is increasing (Fisher et al. 2006b). Oxygen conditions in the Choptank, therefore, are somewhat similar to those in Chesapeake Bay in an earlier era, and an understanding of the forcing of eutrophication in the Choptank may provide useful information on the Chesapeake and other systems undergoing eutrophication, such as the Delmarva coastal bays (Wazniak et al. 2004). ...
... Increased nitrogen loading to coastal ecosystems has been identified as a key factor in the eutrophication of coastal and estuarine ecosystems (Taylor et al 1995). Nitrogen is often cited as the limiting nutrient in coastal ecosystems (Fisher 2006) and considerable efforts have been dedicated to understanding the role of internal cycling processes in the fate of nitrogen. In ecosystems such as the Chesapeake Bay, the major N sinks include burial in sediments, denitrification, and export to the ocean . ...
... The stations in each basin were chosen to be similar in water depths near the axis of the channel. This portion of the Choptank River does not experience bottom water anoxia or hypoxia (Fisher et al. 2006) and oxidized surface sediments were observed at all sites and at all times throughout this study. The HP paired sites were in 12 m of water and consisted of very fine-grained sediment. ...
... The Choptank River watershed covers 252 km 2 and is heavily dominated by agriculture. Primary production is nitrogen limited in the river except in early spring when high nitrate concentrations from upstream sources persist over much of the river (Fisher et al. 2006). Our study site was located in the mesohaline portion of the Choptank River (Figure 2.1). ...
... As a result, BMPs are subsidized by agencies such as the US Dept. of Agriculture and state agencies with incentive payments and "cost-shares" to partially off-set costs to the farmer. Reductions in diffuse nutrient pollution are more challenging and are typically quantified by monitoring of atmospheric deposition or single land uses (e.g., Reckhow et al. 1980;Beaulac and Reckhow 1982;Clesceri et al. 1986;Clark et al. 2000;Schlesinger and Bernhardt 2014), by comparing watersheds with varying amounts of land uses (e.g., Jordan et al. 2003;Fisher et al. 2006aFisher et al. , 2010, or by hydrochemical modeling (e.g., Lee et al. 2001;Alexander et al. 2002). ...
... Eutrophication of the Choptank estuary (Fisher et al. 2006a) is a microcosm of eutrophication in Chesapeake Bay as a whole. For example, agriculture and forests are the dominant land uses in both the Choptank and Chesapeake basins, and population density in the Choptank (59 km −2 in 2000, 52 km −2 in 2010; Fisher et al. 2006a) is similar to other Chesapeake basins (30-70 km −2 ; Carlozo et al. 2008). ...
... Eutrophication of the Choptank estuary (Fisher et al. 2006a) is a microcosm of eutrophication in Chesapeake Bay as a whole. For example, agriculture and forests are the dominant land uses in both the Choptank and Chesapeake basins, and population density in the Choptank (59 km −2 in 2000, 52 km −2 in 2010; Fisher et al. 2006a) is similar to other Chesapeake basins (30-70 km −2 ; Carlozo et al. 2008). As for the Chesapeake (e.g., Kemp et al. 2005), the degradation of the Choptank estuary is well documented (e.g., Staver and Brinsfield 1996;Newell et al. 2004;Benitez and Fisher 2004;Fisher et al. 2006a, b;Sutton et al. 2009). ...
Article
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Chesapeake Bay has a long history of nutrient pollution resulting in degraded water quality. However, we report improvements in chlorophyll a in surface waters and dissolved oxygen in bottom waters at one of three estuarine stations in the Choptank tributary of Chesapeake Bay. We updated a previous nutrient budget for the estuary constructed for reference year 1998 using rates of atmospheric deposition, inputs of watershed diffuse sources (primarily agriculture), and discharges of point sources (primarily human waste) for reference year 2017. Parallel trends suggest that improvements in water quality at the one station were likely due to 20% reductions in direct atmospheric deposition on the estuary’s surface and 78–95% reductions in wastewater N and P due to installation of tertiary treatment. The agricultural sector, the dominant source of N and P, appeared to provide little contribution to improved water quality during this period. Although efforts to reduce nutrient losses from agriculture are common throughout the Choptank basin, widespread reductions from agricultural diffuse sources could make large contributions to improved water quality at all stations in the estuary. The response in the Choptank is similar to those observed elsewhere in the USA, Europe, Australia, and New Zealand due to improved wastewater treatment. Similar to our findings, the upper Potomac River of Chesapeake Bay saw improvements driven by reductions in atmospheric deposition. Unfortunately, few studies elsewhere have shown improvements in water quality due to agricultural management. The data presented here indicate that public and industrial investments in reductions of atmospheric emissions and upgrades to wastewater treatment plants have improved estuarine water quality in the Choptank.
... They are frequently exposed to anoxic conditions, whether through air exposure during emersion in the intertidal zone, or during the summer when water temperatures drive dissolved oxygen in the bottom waters to low levels (Widdows et al., 1979;Lenihan et al., 1995). In the Chesapeake Bay, hypoxia has been driven by anthropogenic sources, including farming runoff from fertilization and animal feces and wastewater treatment plants (Kemp et al., 2005;Fisher et al, 2006). ...
... The conditions necessary for the development of a "dead zone" of hypoxic water are stratification of the water column, which prevents mixing of the oxygenated surface layer with the oxygen-poor bottom waters, and the breakdown of organic matter in the bottom waters. Bacterial decomposition of organic matter uses up the oxygen in the already oxygen depleted bottom waters, and stratification prevents replenishing bottom waters with oxygen from the surface layers (Taft et al., 1980;Nixon, 1995;Fisher et al., 2006). ...
... Additionally, authors argue that the issue of hypoxic and anoxic conditions in the bottom is a recent phenomenon recorded during the last fifty years (Ibid). Since the average temperature during the summer is high (compared to BSR) the phytoplankton growth and event of eutrophication is even more threatening Bay's ecosystems and biodiversity (Fisher, et al. 2006). According to Fisher et al. (2006) P and N leakage to the water column have increased 2-5 times from the timespan between 1970-2004 and around 4-20 times during the last 350 years (a.a., p. 435). ...
... Since the average temperature during the summer is high (compared to BSR) the phytoplankton growth and event of eutrophication is even more threatening Bay's ecosystems and biodiversity (Fisher, et al. 2006). According to Fisher et al. (2006) P and N leakage to the water column have increased 2-5 times from the timespan between 1970-2004 and around 4-20 times during the last 350 years (a.a., p. 435). ...
Thesis
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The Baltic Sea is the most polluted sea in the world. Its hydrological conditions and ongoing eutrophication are a high threat for marine biodiversity and ecosystems. Additionally, eutrophication has negative effects on the wellbeing of countries and their societies in the Baltic Sea Region (BSR). Actions to mitigate eutrophication in the Baltic Sea have been implemented through on-land measures in the last 40 years. Although the improvement in the marine environment is notable, it happens very slowly. In order to combat eutrophication, there is a need for a combination of on-land and in-situ measures. In this study, blue mussel farming practices are presented as one of the in-situ measures to combat eutrophication in the Baltic Sea. Blue mussel farming has been implemented in Sweden since the 1980s and has potential to not only mitigate the amounts of nutrients that accumulate in the sea but also brings a circular approach to resource use. In this study, stakeholders from four different sectors that are closely related to blue mussel farming practices and Baltic Sea issues have been interviewed with the aim of making a comprehensive analysis of stakeholder perceptions of blue mussel farming practices in the BSR. Interviewed stakeholders represent four different sectors - academia, entrepreneurs, municipalities and NGOs. A comprehensive analysis of stakeholders’ perceptions on blue mussel farming practises from environmental, social and economic perspective is presented. All interviewed stakeholders are actors in Sweden and represent Swedish perspective on blue mussel farming activities. Potential causes for different perceptions across sectors are discussed.
... Urbanization results in an increase in built-up land and impervious surfaces, which then further change the runoff process and cause water pollution (Johnes, 1996;Johnson et al., 1997;Pratt and Chang, 2012;White and Greer, 2006). Arable land, which is characterized by agricultural activities that export phosphorus and nitrogen, makes a large contribution to nutrients in the water (Ahearn et al., 2005;Broussard and Turner, 2009;Fisher et al., 2006;Mander et al., 2000b;Motavalli et al., 2008). Conversely, forested land can trap and filter water pollutants and improve water quality (Brett et al., 2005;Galbraith and Burns, 2007;Lopez et al., 2008;Postel and Thompson, 2005). ...
... Without intensity information, our study verified that land use proportion was a useful indicator for correlating with water quality. It shows that arable land and residential land proportions have a positive correlation with water quality parameters, and that forest proportion is negatively correlated with water quality, which is in line with previous studies (Ahearn et al., 2005;Brett et al., 2005;Broussard and Turner, 2009;Fisher et al., 2006;Lopez et al., 2008;Mander et al., 2000b). The negative correlation between forests and water nutrient concentration may be explained by two factors. ...
... These relationships may be driven by several potential mechanisms (Fig. 10). Cropland is strongly tied to non-point nutrient pollution (i.e., eutrophication) in coastal systems (Jordan et al. 1997), which can increase plankton production and lead to hypoxia (Kemp et al. 2005;Diaz & Rosenberg 2008) and can reduce coverage and density of SAV by decreasing water clarity and promoting growth of epiphytic algae (Fisher et al. 2006;Patrick et al. 2014). We found evidence for this in our study, where increasing % watershed cropland was linked with nutrient enrichment and reduced dissolved oxygen as well as scarcity of SAV and nearshore wetlands. ...
... The three generalized functional species groups are circled relationships between planktivore abundance, cropland cover, and TN are consistent with studies showing that planktivores respond positively to high nutrient loads because of greater amounts of plankton (Caddy 1993;de Leiva Moreno et al., 2000). Elevated TN levels also likely contribute to negative relationships between benthivore-piscivores and cropland by stimulating planktonic and epiphytic algal blooms (Fisher et al. 2006) and thereby reducing water clarity, which in turn reduces SAV density and impedes foraging efficiency for visual predators (Henley et al. 2000). This argument is substantiated by negative interactions between SAV and TN observed in models for all species whose abundance was related to cropland (significant for spot and Atlantic croaker). ...
Article
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Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments.
... The Choptank River is a wide, relatively shallow tributary on the eastern side of the Chesapeake Bay, USA (Fig. 1a). The surface area is approximately 300 km 2 and mean depth is 3.6 m (Fisher et al., 2006). The salt-intrusion length is 60-70 km (Fisher et al., 2006), and the median monthly streamflow (Jun-Aug) is 1.25 m 3 s -1 (USGS Greensboro, MD), which can drive two-layer estuarine circulation (Goodwin, 2015). ...
... The surface area is approximately 300 km 2 and mean depth is 3.6 m (Fisher et al., 2006). The salt-intrusion length is 60-70 km (Fisher et al., 2006), and the median monthly streamflow (Jun-Aug) is 1.25 m 3 s -1 (USGS Greensboro, MD), which can drive two-layer estuarine circulation (Goodwin, 2015). The river experiences semi-diurnal tides. ...
Article
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Despite strong control over marine plankton dynamics and negative impacts on human activities, jellyfish are not well quantified due primarily to sampling difficulties with nets. Therefore, some of the longest records of jellyfish are visual shore-based surveys. As surface counting is inexpensive and simple, it is of interest to determine what can be learned from such records as well as the usefulness of the method. We analyzed a 4-year high-frequency time series of Chrysaora quinquecirrha medusa counts collected using three sampling methods in the Choptank River, Chesapeake Bay. Medusa abundance was modeled by change points and was highly correlated between the sampling methods. The remaining signal was random, and indices of aggregation [fit to the Poisson distribution, Taylor’s Power Law (TPL), and Morisita’s Index] indicated that medusae were aggregated. TPL suggested that patches grew in the number of individuals as abundance increased. Additionally, a simple conceptualization of where the time series sampled in space revealed that the upper bound of patch size was on the order of kilometers. Our results enhance the knowledge of local C. quinquecirrha abundance and patchiness, alluding to processes that generate these patterns. This study also provides direction for improving population monitoring from visual shore-based surveys.
... One of the principal and most common environmental problems found in estuaries is an excess of nutrients induced by human activities, which is known as cultural eutrophication (Hasler, 1947). This condition has been detected in estuaries worldwide, in both developing and developed countries, such as China, India, Brazil, Russia, United States, and Australia (Fisher et al., 2006;Martin et al., 2008;Aleksandrov, 2010;Santiago et al., 2010;De et al., 2011;Cheng et al., 2012). ...
... While eutrophication is considered to be a disturbance rather than a form of pollution, the trophic status of aquatic ecosystems has been considered a good indicator of environmental health, and has been used as a diagnostic tool to characterize the water quality status of many aquatic ecosystems, including polluted estuaries (Kennish et al., 2013). 1 Treated wastewater 2 Untreated wastewater *Estimated by Lacerda (2006) Thus, a eutrophication may occur as a natural process over the course of a period of thousands of years, when the waters gradually age and become more productive due to the accumulation of nutrients and organic biomass or through the anthropogenic input of nutrients from point and nonpoint sources, referred to as cultural eutrophication (Mannion, 2014 (Fisher et al., 2006;Martin et al., 2008;Santiago et al., 2010;Aleksandrov, 2010;De et al., 2011;Cheng et al., 2012). ...
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In the Amazon region, few data are available on the impacts caused by the urban settlements found in the proximity of estuaries. In the estuary of the Caeté River, the focus of the present study, the nutrient input is controlled by both natural features and anthropogenic disturbances generated by local communities. In this context, the principal aim of the study was to analyze the quality of the water of the Caeté estuary, and the relative contribution of natural and anthropogenic forcings. To this end, climatological, hydrodynamic and hydrological features were monitored, and potential sources of pollution were identified in the different sectors of the Caeté estuary. Potential future scenarios for the estuary are also described, based on the analysis of anthropogenic and natural processes, which may contribute to the quality of its waters. The results indicate higher levels of nutrient input in the upper sector of the estuary, where 90% of the local population is concentrated, and most of the region’s commercial activities (e.g., public markets, ice factories, and docking facilities) are found. As a consequence, eutrophic waters with high concentrations of faecal coliforms (up to 1100 MPN/100 ml) were observed during spring tides in the dry season when the transport and dilution of the estuary’s waters are less effective. Eutrophication also occurred to a lesser extent in the other (middle and lower) estuary sectors, although in this case, the results indicate the influence of natural processes, reflecting the high nutrient concentrations of this Amazonian region. During neap tides, eutrophication was less pronounced, and water quality was improved in both dry and rainy seasons. A comparative analysis showed that, under similar conditions of the flood cycle, the trophic status of the estuary varied little between spring and neap tides. As the population of the region surrounding the Caeté estuary is increasing by 10–20% per decade, resulting in a significant increase in human pressures and impacts on the study area. The current eutrophication status of the estuary may have permanent effects, which may be aggravated during the dry season or drought events, when the estuary is more vulnerable to the retention of nutrients. The water quality of the Caeté Estuary can be improved by the implementation of the following measures: (i) urban planning to control the discharge of sewage, (ii) the construction of water treatment plants to reduce the input of untreated effluents, and (iii) the introduction of regulations for the use of water based on its current quality.
... Species are not always found in suitable habitat and may sometimes occur in sites deemed unsuitable. Conditions in the Maryland Coastal Plain are the product of the impacts and legacies of four centuries of land conversion ( Foresman et al., 1997;Benitez and Fisher, 2004;Fisher et al., 2006). This makes it impossible to know the original distribution of A. heterodon and if it exists at present in favourable habitats or as relicts in remnant habitats on the way to extirpation in highly altered systems. ...
Article
• Species distribution modelling can be useful for the conservation of rare and endangered species. Freshwater mussel declines have thinned species ranges producing spatially fragmented distributions across large areas. Spatial fragmentation in combination with a complex life history and heterogeneous environment makes predictive modelling difficult. • A machine learning approach (maximum entropy) was used to model occurrences and suitable habitat for the federally endangered dwarf wedgemussel, Alasmidonta heterodon, in Maryland's Coastal Plain catchments. Landscape‐scale predictors (e.g. land cover, land use, soil characteristics, geology, flow characteristics, and climate) were used to predict the suitability of individual stream segments for A. heterodon. • The best model contained variables at three scales: minimum elevation (segment scale), percentage Tertiary deposits, low intensity development, and woody wetlands (sub‐catchment), and percentage low intensity development, pasture/hay agriculture, and average depth to the water table (catchment). Despite a very small sample size owing to the rarity of A. heterodon, cross‐validated prediction accuracy was 91%. • Most predicted suitable segments occur in catchments not known to contain A. heterodon, which provides opportunities for new discoveries or population restoration. These model predictions can guide surveys toward the streams with the best chance of containing the species or, alternatively, away from those streams with little chance of containing A. heterodon. • Developed reaches had low predicted suitability for A. heterodon in the Coastal Plain. Urban and exurban sprawl continues to modify stream ecosystems in the region, underscoring the need to preserve existing populations and to discover and protect new populations. Copyright © 2016 John Wiley & Sons, Ltd.
... b Positive MBE (Mass balance error) indicates underestimation. development nationally ( Borah et al., 2006) and in the mid-Atlantic and northeast regions ( Fisher et al., 2006;Li et al., 2009). ...
... Cultural eutrophication has been detected in estuaries worldwide, from developing to developed countries (e.g., China, India, Brazil, Russia, United States, and Australia) (Fisher et al., 2006;Martin et al., 2008;Santiago et al., 2010;Aleksandrov, 2010;De et al., 2011;Cheng et al., 2012). In order to reduce this impact on estuarine environments, countries are progressively adopting measures to decrease nutrient loads from point and diffuse sources. ...
... The cycling of nutrients in coastal systems has been frequently affected by anthropogenic fertilization, implying in coastal primary production fueling (Fisher et al., 2006;Carstensen et al., 2011) and elevated nutrient accumulation within sediments (Church et al., 2006;Borges et al., 2009). Nutrient regeneration to surface water from underlying sediments has been postulated as a factor that influence the coastal primary production if these elements are not efficiently removed from pore waters by sorption and precipitation processes in the upper sediment layers (Rozan et al., 2002;Ogrinc and Faganeli, 2006). ...
... Historically, episodic hypoxia and anoxia occurred in deeper portions of the water column of the Chesapeake Bay (Cooper and Brush 1991;Cronin and Vann 2003;Hagy et al. 2004). Since precolonial times, total nitrogen and total phosphorus loadings to the Bay are estimated to have increased 6.2-fold and 17.1-fold, respectively (Boynton et al. 1995), with much of the increase having occurred over the last century (Hagy et al. 2004;Kemp et al. 2005;Fisher et al. 2006); bottom-water hypoxia is now a persistent, annual occurrence. Nutrient loadings have increased because of a threefold increase in human population size within the Bay watershed over the past 100 years, changing land-use patterns (initially forested, followed by large-scale clearing for agriculture, today agricultural lands are decreasing as land becomes urbanized or reverts to forests), and an increase in the use of agricultural fertilizers with the use of nitrogen-based fertilizer in Maryland doubling between 1960and 2000(Kemp et al. 2005. ...
Chapter
Water quality in the Chesapeake Bay has decreased since the 1950s due to an increase in nutrient loadings that have increased the extent and duration of hypoxic conditions. Restoration via large-scale reductions in nutrient loadings is now underway. How reducing nutrient loadings will affect water quality is well predicted; however, the effects of reduced nutrients (reduced food availability) and associated reduced hypoxia on fish are generally unknown as most water quality models do not include trophic levels higher than zooplankton. We dynamically coupled a spatially explicit, individual-based population dynamics model of juvenile and adult anchovy to the three-dimensional Chesapeake Bay eutrophication model. Growth rates of individual anchovy were calculated using a bioenergetics equation. Anchovy consumption rates were forced by zooplankton densities from the water quality model, and anchovy consumption of zooplankton was added as an additional mortality term on zooplankton in the eutrophication model. Anchovy mortality was size dependent and their movement depended on water temperature, dissolved oxygen, and zooplankton concentrations. Multi-year simulations with fixed annual recruitment were performed under decreased, baseline, and increased nutrient loadings scenarios. The results of our analyses show that anchovy responses to changed nutrient loadings are dominated by changes in productivity, including simultaneous changes in growth and mortality rates, and spatial distribution, and depend on life stage. As such, we recommend using full life cycle, spatially explicit population models that are dynamically coupled to water quality models as a tool for predicting the effects of changes in nutrient loadings on fish population dynamics. <a PDF version of the manuscript is available if you ask me for it through researchgate or by email at aaron.adamack@gmail.com>
... Most studies on eutrophication processes have been conducted in temperate waters (Lillobø et al. 2005;Fisher et al. 2006;Howard and Marino 2006), with only a few studies in subtropical and tropical waters (NRC 2000). Subtropical and tropical waters in southeast Asia are quite different ecosystems in terms of the high N:P ratios in riverine inputs into coastal waters and hence, phosphorus appears to be the most limiting nutrient in contrast to nitrogen in temperate waters. ...
Article
Full-text available
Phytoplankton biomass and bottom dissolved oxygen are controlled by processes such as residence time/exchange between a bay and the open ocean, vertical mixing/stratification, the most limiting nutrient/nutrient ratios, light penetration and grazing as well as climate variability. We examined the eutrophication processes and the drivers that regulate these processes by comparing three semi-enclosed bays (Port Shelter, Tolo Harbour, and Deep Bay) with different buffering capacities using long-term water quality data, including chlorophyll and dissolved oxygen along with salinity, temperature, and nutrients. The outer part of Port Shelter is wide open to southern coastal waters and has a residence time of about 20 days, but it is relatively pristine, with little input of sewage effluent. Nutrient concentrations are as low as chlorophyll a values. Tolo Harbour in northeast waters is a land-locked bay/inlet with high nutrients, a long 28-day residence time, and year-round stratification; hence, it is very vulnerable to eutrophication. Phytoplankton biomass has not reached the potential maximum that could be produced from the high ambient nutrient concentrations, suggesting that top-down control by grazing as well as turbidity is affecting the system. Deep Bay, in western waters between mainland China and Hong Kong, receives sewage input from the city of Shenzhen with up to 500 µM DIN at the head of the bay. However, there is no hypoxia and phytoplankton biomass is not as high as one would expect from such high nutrient levels. Turbidity, light limitation, and top-down control by benthic grazing likely play an important role in reducing the magnitude and frequency of phytoplankton blooms. Deep Bay receives the highest nutrient loads of the three bays, but eutrophication impacts are greatly reduced due to the aforementioned controls.
... As other power sources replaced water-powered mills, the milldams were abandoned and breached, and the streams incised into thick, longitudinally continuous sequences of fill sediments that had accumulated along the valley bottoms during the seventeenth to nineteenth centuries. Mobilization of this sediment has created concerns about water quality in nearshore areas drained by these watersheds, particularly Chesapeake Bay, where sedimentation and high nutrient loading have endangered commercial fisheries and created eutrophication (Fisher et al., 2006). Prior to the work by Walter and Merritts (2008), the widespread assumption was that excess sediments and nutrients resulted from continued upland farming, and that resource management should focus on reducing upland sediment yields and restoring forested riparian corridors. ...
... All upstream water quality variables fell within ranges reported in previous studies conducted in the Choptank River estuary (Fisher et al., 2006;Glibert et al., 2001;Stevenson et al., 1993). The average TAN excretion rate determined in the excretion experiment portion of the study falls within the range of excretion rates determined in previous studies (Table 1), and is slightly higher than the rates given by Srna and Baggaley (1976) and Hammen (1968) in laboratory studies, and lower than the rates given by Dame et al. (1992) and Pietros and Rice (2003), which were field and mesocosm experiments, respectively. ...
... To develop information on habitat conditions for individual striped bass, we combined high-resolution water quality surveys with depth telemetry of fish from the Patuxent River estuary, a sub-estuary of Chesapeake Bay with persistent stratification and seasonal hypoxia (Breitburg et al. 2003;Fisher et al. 2006). The telemetry results were a subset of data from Wingate et al. (2011) on striped bass that were implanted with depth transmitting tags (Vemco®; model V16P-4H-S256; other fish in this study had identification tags only). ...
Article
In many stratified coastal ecosystems, conceptual and bioenergetics models predict seasonal reduction in quality and quantity of fish habitat due to high temperatures and hypoxia. We tested these predictions using acoustic telemetry of 2 to 4 kg striped bass (Morone saxatilis Walbaum) and high-resolution spatial water quality sampling in the Patuxent River, a sub-estuary of the Chesapeake Bay, during 2008 and 2009. Striped bass avoided hypoxic (dissolved oxygen ≤2 mg·l1) subpycnocline waters, but frequently occupied habitats with high temperatures (>25 °C) in the summer months, as cooler habitats were typically not available. Using traditional concepts of the seasonal thermal-niche oxygen-squeeze, most of the Patuxent estuary would be considered unsuitable habitat for adult striped bass during summer. Application of a bioenergetics model revealed that habitats selected by striped bass during summer would support positive growth rates assuming fish could feed at one-half ofmaximum consumption. Occupancy of the estuary during summer by striped bass in this study was likely facilitated by sufficient prey and innate tolerance of high temperatures by sub-adult fish of the size range that we tagged. Our results help extend the thermalniche oxygen-squeeze hypothesis to native populations of striped bass in semi-enclosed coastal systems. Tolerance of for supraoptimal temperatures in our study supports recent suggestions by others that the thermal-niche concept for striped bass should be revised to include warmer temperatures.
... However they estimated that fertilizer inputs of N were greater than those from urban areas, and that they also contributed between about 50 ± 10% of the net anthropogenic N inputs into the basin as a whole. Numerous studies (Jordan et al., 1997;Filoso et al., 2003;Fisher, 2006) have found a positive correlation between total N discharge and percentage of cropland and that could be attributed to the strong positive correlation between total N inputs and percent of catchment in agricultural land (Boyer et al., 2002). Developed (urban and/or agricultural) catchments thus have high nitrogen export due to human activities that change N cycle by increasing the transfer from the vast and unreactive atmospheric N to biologically available forms on land (termed N fixation) (Ayers et al. 1994;Galloway et al. 1995). ...
... Drainage and irrigation recycling infrastructure problems resulting from eutrophication include increased filter clogging (for irrigation systems using recycled surface water) and increased maintenance of drainage ditches and reservoirs owing to excessive production of algae and aquatic plants. Off-nursery discharge of nitrate-N-enriched drainage water, especially into N-limited aquatic ecosystems, may result in loss of desirable aquatic habitats and undesirable changes to natural ecosystems due to eutrophication (Carpenter, 2005;Fisher et al., 2006;Hart et al., 2004;Howarth and Marino, 2006;Livingston, 2007;Mitsch et al., 2001). Nitrogen concentrations greater than 0.4 mgÁL -1 have been shown to accelerate eutrophication (Taylor et al., 2006;Vitousek et al., 1997;Wetzel, 1983), cause harmful algal blooms (Rabalais et al., 1996;Taylor et al., 2006), and cause eelgrass (Zostera marina) declines (Burkholder et al., 1992;Taylor et al., 2006). ...
Article
Nitrate-nitrogen (N) losses in surface drainage and runoff water from ornamental plant production areas can be considerable. In N-limited watersheds, discharge of N from production areas can have negative impacts on nontarget aquatic systems. This study monitored nitrate-N concentrations in production area drainage water originating from a foliage plant production area. Concentrations in drainage water were monitored during the transition from 100% reliance on fertigation using urea and nitrate-based soluble formulations (SF) to a nitrate-based controlled-release formulation (CRF). During the SF use period, nitrate-N concentrations ranged from 0.5 to 322.0 mg L-1 with a median concentration of 31.2 mg L-1. Conversely, nitrate-N concentrations during the controlled-release fertilization program ranged from 0 to 147.9 mg L-1 with a median concentration of0.9 mg L-1. This project demonstrates that nitrate-N concentrations in drainage water during the CRF program were reduced by 94% to 97% at the 10th through 95th percentiles relative to the SF fertilization program. Nitrate-N concentrations in drainage water from foliage plant production areas can be reduced by using CRF fertilizer formulations relative to SF formulations/fertigation. Similar results should be expected for other similar containerized crops. Managers located within N-limited watersheds facing N water quality regulations should consider the use of CRF fertilizer formulations as a potential tool (in addition to appropriate application rates and irrigation management) for reducing production impacts on water quality.
... The Choptank River estuary covers ~ 300 km 2 with a mean water depth of 3.6 meters and is characterized by high algal biomass derived from both non-point and point N and P inputs. The Choptank River is 26 meters deep at its maximum and is separated at its mouth from the Chesapeake Bay by a sediment sill (Fisher et al. 2006). The transect site at Horn Point Laboratory was located on a north-facing shoreline, with water depths ranging from 0 to 3 meters. ...
... Sterner 2008). In estuaries, there is evidence of temporal and spatial changes in the limiting nutrients (D'Elia et al.1986;Domingues et al. 2005;Fisher et al. 2006). A switch from phosphorus limitation in spring to nitrogen limitation during summer is often observed in estuarine systems (D'Elia et al. 1986;Pennock and Sharp 1994;Fisher et al. 1999). ...
Article
A first survey was done on algae present in the Sundays River from its source to its confluence with the sea. Species found in the upstream sections of the river included indicators of good water quality, but the quality deteriorated downstream with peaks in algal abundance being ascribed to peaks in nutrient concentrations. Cyanobacteria and euglenoids were present in the upper and middle reaches of the river, but were absent downstream. Dinoflagellates became more important downstream, especially in the estuary. Dominant species, reaching high concentrations along the river, included Nitzschia frustulum, Nitzschia capitellata, Carteria klebsii, Chlorella vulgaris and Anabaena species. The presence of the diatom Eolimna comperei is a first record of its occurrence in South Africa. The Sundays River can be described as a brackish, hard water system with high nutrient concentrations in certain sections. The most important contributors to high nutrient concentrations were point sources in the vicinity of towns along the river banks, as well as diffuse sources contributing to high nitrogen concentrations in the fertile Sundays River valley. Increasing salinities were due to pollution, evaporation and agricultural activities in the valley.
... (Torres-Valdes and Purdie, 2006 and is fed by nutrients loads from the Test and Itchen Rivers discharge with an average annual 1.54 x10 6 m 3 day -1 in addition to sewage discharge (Hydes, 2000). Evidently, nutrients are significant indicators of the riverine and anthropogenic input (Townsend et al., 1994;Fisher et al., 2006;Sin et al., 2013). In present study, relatively high concentrations of nitrate, phosphate and silicate, were observed at early 68 sampling period between late winter (February) until mid-spring (April) nitrate averaged between 78.4 and 93.4 µmol L -1 , and declined during mid-July to 10.9 ...
Thesis
Frequent measurements of the physical‐chemical parameters and biologicalcomponents of estuaries are key for assessing the ecological status of thesetransitional waters. Little is known about the microbial community composition oftwo temperate South Coast UK estuaries, Southampton Water and ChristchurchHarbour (Mudeford Quay). The aim of this research project was to investigate howchanges in the abundance and dynamics of the dominant phylogenetic heterotrophicbacteria populations relate to major physical‐chemical parameters duringphytoplankton bloom periods in the spring and summer months in these twoestuaries.During 2013 in Southampton Water, the spring phytoplankton bloom occurred whenthe water temperature was below 10°C whereas in Christchurch Harbour it occurredat 14°C, and in the following years in Southampton Water at 14 °C and 15 °C, in 2014and 2015, respectively. The spring bloom chlorophyll a concentrations inSouthampton Water never exceeded 10 μg L‐1 in all three years while in ChristchurchHarbour a major peak in spring 2013 reached 44 μg L‐1. Surface salinity inSouthampton Water showed a narrow range of 27‐33 whereas, at Mudeford Quay atthe entrance to Christchurch Harbour a much larger range was detected of 1.3‐22.The concentration of inorganic nutrients detected between the two estuaries fornitrate, phosphate and silicate had a much higher range in Christchurch Harbourcompared to Southampton Water reflecting the contribution from different riversources. Identifying the biological components the influence of the physical‐chemicalcontrols affecting their dynamics and succession. The phytoplankton community inSouthampton Water was assessed from HPLC pigment analysis coupled withmicroscopic counts, and indicated diatoms (Skeletonema sp., Thalassiosira sp., andChaetoceros sp.) dominated the spring bloom and dinoflagellates dominated summerbloom with major species Scripsiella sp. and Prorocentrum sp.Nucleic acid staining (DAPI and SYBR Green I) was applied to 1% (PFA) preservedwater samples for total enumeration of bacterioplankton. A cytosense flowcytometry slightly overestimated the concentration of bacteria compared to DAPIcell counts determined using a fluorescent microscope mainly during thephytoplankton spring and summer blooms but overall with significant correlationbetween the two methods for Southampton Water and Christchurch Harbour (r =0.87, r = 0.85, p <0.0001, n = 32 respectively). Fluorescence in situ hybridization(FISH) with oligonucleotide probes was used to determine the abundance anddominance of various heterotrophic bacteria groups in samples from both estuariesand theses related to environmental conditions. Betaproteobacteria showed a strongnegative significant correlation with salinity (r = ‐0.95, p <0.0001, n = 29) in the twoestuaries indicating they favour fresh water systems. Alpha‐, andGammaproteobacteria were detected with variable significant correlation withtemperature and salinity. However, only a moderate correlation was observedbetween the phylogenetic groups and Chl‐a concentrations highlighting the fact thatheterotrophic bacteria may utilize organic carbon from other sources in theestuarine system. A principal component analysis (PCA), indicated temperature tobe the most influence on bacteria domain levels (Eubacteria and Euryarchaea).Whereas, at phylogenetic class level proteobacterial phyla, salinity and Chl‐a werethe most influence on their abundance and succession.
... Indeed, despite a reduction in point source nutrient inputs in the Patuxent River watershed, summer phytoplankton blooms in the lower Patuxent River estuary have persisted [44]. Recent studies suggest that the dominant nutrient source driving this observed productivity has shifted from watershed-based to Chesapeake Bay-oriented [44,45]. Our data do not have the temporal resolution needed to tease out the potential influence of tides on the observed trends. ...
Article
Full-text available
Fowler’s Sneaker Depth (FSD), analogous to the well known Secchi disk depth (Zsd), is a visually discerned citizen scientist metric used to assess water clarity in the Patuxent River estuary. In this study, a simple remote sensing algorithm was developed to derive FSD from space-borne spectroradiometric imagery. An empirical model was formed that estimates FSD from red-end remote sensing reflectances at 645 nm, Rrs(645). The model is based on a hyperbolic function relating water clarity to Rrs(645) that was established using radiative transfer modeling and fine tuned using in-water FSD measurements and coincident Rrs(645) data observed by NASA’s Moderate Resolution Imaging Spectroradiometer aboard the Aqua spacecraft (MODISA). The resultant FSD algorithm was applied to Landsat-8 Operational Land Imager data to derive a short time-series for the Patuxent River estuary from January 2015 to June 2016. Satellite-derived FSD had an inverse, statistically significant relationship (p<0.005) with total suspended sediment concentration (TSS). Further, a distinct negative relationship between FSD and chlorophyll concentration was discerned during periods of high biomass (> 4 μg L−1 ). The complex nature of water quality in the mid-toupper Chesapeake Bay was captured using a MODISA-based FSD time series (2002-2016). This study demonstrates how a citizen scientist-conceived observation can be coupled with remote sensing. With further refinement and validation, the FSD may be a useful tool for delivering scientifically relevant results and for informing and engaging local stakeholders and policy makers.
... Nutrient loading from freshwater is considered as one of the main sources of eutrophication in estuary coasts (Fisher et al., 2006;Clarke et al., 2006). Increase in nutrient loading to coastal waters is related to rapid increase in the total and urban population (Billen et al., 2007) and to the increase of atmospheric nitrogen deposition rate (Scudlark et al., 2005), frequency and intensity of precipitation (Yin and Harrison, 2008). ...
Article
Full-text available
We investigated nutrient loading and trophic states in a coastal estuarine system in the Asan estuary by assessing phytoplankton biomass and using the trophic index (TRIX). The monthly and yearly nutrient loading (TN, TP) from freshwater discharge from the Asan and Sapgyo reservoirs into the estuary were estimated and analyzed with related factors. Monitoring data (physio-chemical and biological variables) collected at five estuary stations were used to assess trophic states. Descriptive statistics of total phytoplankton cells, chl a concentrations and primary productivity were also used to assess seasonal trophic status. N loading from freshwater ranged 1.0~1.3×104 ton yearly. The yearly P loading ranged between 350 and 400 ton during 2004~2006, increasing to 570 ton in 2007. Regression results suggest that DIN and DSi were correlated with freshwater discharge at the upper region. Based on phytoplankton biomass and total cell abundance, the trophic state of the estuary was found to be eutrophic during spring due to phytoplankton bloom. Primary productivity level was remarkably high, especially in summer coinciding with high nutrient loading. Pheopigments increased during warm seasons, i.e. summer and fall. Trophic index results indicate that the trophic state varied between mesotrophic and eutrophic in the estuary water body, especially in the upper region. The results suggest that phytoplankton production was regulated by nutrient loading from freshwater whereas biomass was affected by other properties than nutrient loading in the Asan Estuary ecosystem.
... All collections were from low marsh habitat, with the marsh plant communities largely set by salinity (Baldwin et al. 2012). The nutrient burial data are most abundant in three areas (9-25 cores from each), with the Patuxent River estuarine gradient receiving nutrient inputs from point sources (Boynton et al. 2008), and both Choptank River and Monie Bay watersheds heavily influenced by agriculture (Fisher et al. 2006). Denitrification data were taken from studies in a number of tidal subestuaries, including the heavily nutrient-impacted Sassafras River (Ana I. Sousa, unpublished data), agriculturally dominated Corsica River (Jeffrey C. Cornwell, unpublished data), Dyke Marsh on the nutrient-enriched upper Potomac River (Hopfensperger et al. 2009), the urban and agriculturally impacted upper Patuxent River (Boynton et al. 2008), and at Poplar Island, a constructed wetland area built using nutrient rich fine-grained dredged materials from the upper Chesapeake Bay navigation channels Staver et al. 2020). ...
Article
The worldwide loss of coastal wetlands has traditionally been addressed as the loss of ongoing nutrient retention ecosystem services. However, nutrient remineralization from eroded particles may further exacerbate water quality degradation. Using data on nutrient burial and denitrification from northern Chesapeake Bay, along with estimates of the bioavailability of eroded marsh particulates, the changing role of wetlands as an important sink for nutrients is examined. Although the erosion of wetlands results in the reintroduction of nitrogen and phosphorus into open-water habitats, the potential for exacerbating eutrophication is highly diminished by the low lability of wetland organic matter. The impact of such erosion on the cycling of Fe-bound phosphorus from marsh soils is highly dependent on both the amount of inorganic P, its solid phase association with Fe, and its potential remobilization from the estuarine sediments into which it is deposited. Although nutrient sequestration in newly constructed wetlands built from dredged materials suggested a rapid development of nutrient sequestration, a better understanding of nutrient ecosystem services provided by marshes created by transgression into uplands is necessary for understanding the long-term nutrient retention value of coastal wetlands.
... Eutrophication occurs naturally over centuries as waterbodies age and are filled in with sediments (Carpenter, 1981). However, human activities have accelerated the rate and extent of eutrophication through both point and non-point source inputs of nutrients such as nitrogen and phosphorus, a process termed "cultural eutrophication" (Fisher et al., 2006). ...
Thesis
Full-text available
Green Bay has become a model ecosystem for the restoration of aquatic macrophytes in degraded freshwater systems. Countless ecosystem stresses challenge Green Bay today, with cultural eutrophication the principal driver of initial and sustained aquatic ecosystem degradation. In response, a significant amount of time and resolve has been invested into the state of Green Bay to improve conditions, namely through watershed level reductions in nutrients and sediment loading. Recent efforts have emerged to actively restore aquatic macrophytes in an attempt to disrupt the within-system positive feedbacks that may be perpetuating an algal dominated eutrophic state, with this study evaluating the restoration potential of northern wild rice (Zizania palustris L.), a native annual grass once historically abundant within Green Bay and its tributaries. The first objective of this study was to document variations in environmental conditions among nineteen potential wild rice restoration sites in Green Bay and to understand relationships among these variables and wild rice restoration success. In agreement with our expectations, principal components analysis suggested significant variation in environmental conditions existed among both wetland complexes and the restoration sites established within wetlands. Distinct environmental differences were driven primarily by differences in water clarity, sediment conditions, and non-restored aquatic vegetation. Furthermore, annual average wild rice cover appeared to be related to these environmental factors. The second objective of this study was to evaluate the seasonal effects of abiotic and biotic factors on wild rice cover, with seasons paralleling discrete growth stages of wild rice. Contrary to our expectations, environmental factors were found to have little seasonality, with the ability of seasonal environmental conditions to predict wild rice cover inferior to or only marginally better than annual environmental conditions with the exception of late summer/ early fall. Late summer/ early fall environmental factors that best predicted wild rice cover included water clarity, submerged aquatic vegetation (SAV) cover, and sediment composition. In other words, restoration sites with greater wild rice cover had relatively greater water clarity, higher SAV cover, and sandy substrates. These results suggest that three simple metrics - water clarity, sediment composition, and SAV - may serve as valuable indicators for successful wild rice restoration sites within Green Bay and furthermore, that the success of a potential restoration site can be reasonably predicted by sampling for these three metrics in late summer/ early fall.
... The over-enrichment of Chesapeake Bay by nutrients has been well recognized and documented (e.g., Fisher et al., 1992Fisher et al., , 2006Boesch et al., 2001;Hagy et al., 2004;Kemp et al., 2005;Brush, 2009). Between the 1950s and 1980s there was an increase in chlorophyll a (Chl a), corresponding to trends in nitrogen (N) loading to the Bay during this period (Kemp et al., 2005), but since the 1990s, these increases have slowed (Harding et al., 2016). ...
Article
Planktonic Prorocentrum, a common harmful dinoflagellate, are increasing in frequency, duration, and magnitude globally, as exemplified by the number of blooms of P. minimum in Chesapeake Bay that have nearly doubled over the past 3 decades. Although the dynamics of transport and seasonal occurrence of this species have been previously described, it has been challenging to predict the timing and location of P. minimum blooms in Chesapeake Bay. We developed a new three-dimensional mechanistic model of this species that integrates physics, nutrient cycling and plankton physiology and embedded it within a coupled hydrodynamic-biogeochemical model originally developed for simulating water quality in eutrophic estuarine and coastal waters. Hindcast simulations reproduced the observed time series and spatial distribution of cell density, in particular capturing well its peak in May in the mid-to-upper part of the estuary. Timing and duration of the blooms were mostly determined by the temperature-dependent growth function, while mortality due to grazing and respiration played a minor role. The model also reproduced the pattern of overwintering populations, which are located in bottom waters of the lower Bay, and are transported upstream in spring by estuarine flow. Blooms develop in the mid-upper parts of the estuary when these transported cells encounter high nutrient concentrations from the Susquehanna River and favorable light conditions. Diagnostic analysis and model-sensitivity experiments of nutrient conditions showed that high nitrogen:phosphorus conditions favor bloom development. The model also captured the observed interannual variations in the magnitude and spatial distribution of P. minimum blooms.
... Nutrient enrichment of aquatic ecosystems typically results in significant alterations in biogeochemical cycling over both space and time [15]. ...
... The effects of wastewater vary due to its various components in different countries. A previous study [63] reported that the low N/P ratio of wastewater inputs resulted in a DIN-limited and DIPsaturated system in the estuaries of Chesapeake Bay, which is totally different from the situation in JZB. Reduced loads of nutrients from the Luggage Point sewage treatment plants into the Moreton Bay resulted in a decrease in DIN concentration and phytoplankton biomass [64]. ...
Article
Full-text available
A marine ecosystem box model was developed to reproduce the seasonal variations nutrient concentrations and phytoplankton biomasses in Jiaozhou Bay (JZB) of China. Then, by removing each of the external sources of nutrients (river input, aquaculture, wastewater discharge, and atmospheric deposition) in the model calculation, we quantitatively estimated its influences on nutrient structure and the phytoplankton community. Removing the river input of nutrients enhanced silicate (SIL) limitation to diatoms (DIA) and decreased the ratio of DIA to flagellates (FLA); removing the aquaculture input of nutrients decreased FLA biomass because it provided less dissolved inorganic nitrogen (DIN) but more dissolved inorganic phosphate (DIP) as compared to the Redfield ratio; removing the wastewater input of nutrients changed the DIN concentration dramatically, but had a relatively weaker impact on the phytoplankton community than removing the aquaculture input; removing atmospheric deposition had a negligible influence on the model results. Based on these results, we suppose that the change in the external nutrients sources in the past several decades can explain the long-term variations in nutrient structure and phytoplankton community. Actually, the simulations for the 1960s, 1980s, and 2000s in JZB demonstrated the shift of limiting nutrients from DIP to SIL. A reasonable scenario for this is the decrease in riverine SIL and increase in DIP from aquaculture that has reduced DIA biomass, promoted the growth of FLA, and led to the miniaturization of the phytoplankton.
... Thus, chlorophyll a, a direct proxy for phytoplankton biomass, is typically used to indicate the trophic status of a coastal ecosystem (Steele 1962;Cullen 1982;Boyer et al. 2009). Elevated phytoplankton biomass is one of the most visible and early symptoms of eutrophication, and long-term increasing trends of phytoplankton biomass (chlorophyll a) can be an indication that nutrient inputs into a system are increasing (Bricker et al. 1999;Fisher et al. 2006;Boyer et al. 2009). ...
Article
Full-text available
Anthropogenic eutrophication threatens numerous aquatic ecosystems across the globe. Proactive management that prevents a system from becoming eutrophied is more effective and cheaper than restoring a eutrophic system, but detecting early warning signs and problematic nutrient sources in a relatively healthy system can be difficult. The goal of this study was to investigate if rates of change in chlorophyll a and nutrient concentrations at individual stations can be used to identify specific areas that need to be targeted for management. Biscayne Bay is a coastal embayment in southeast Florida with primarily adequate water quality that has experienced rapid human population growth over the last century. Water quality data collected at 48 stations throughout Biscayne Bay over a 20-year period (1995-2014) were examined to identify any water quality trends associated with eutrophication. Chlorophyll a and phosphate concentrations have increased throughout Biscayne Bay, which is a primary indicator of eutrophication. Moreover, chlorophyll a concentrations throughout the northern area, where circulation is restricted, and in nearshore areas of central Biscayne Bay are increasing at a higher rate compared to the rest of the Bay. This suggests increases in chlorophyll a are due to local nutrient sources from the watershed. These areas are also where recent seagrass die-offs have occurred, suggesting an urgent need for management intervention. This is in contrast with the state of Florida listing of Biscayne Bay as a medium priority impaired body of water.
... Mismanaged agricultural activities are directly associated with the increase of organic matter, nutrients, turbidity and dead zones in estuaries (Fisher et al., 2006;Yoon et al., 2003;Toledo et al., 2002;Pathak et al., 2004). In the MES, the agricultural area is four times larger than the estuary, but it is concentrated around the internal region, where the most eutrophic conditions were found. ...
... Excess nitrate in groundwater-fed streams and rivers (in conjunction with phosphorus) negatively affects water quality by causing eutrophication in downstream lakes and estuaries, providing suitable conditions for harmful algal blooms, loss of submerged aquatic vegetation due to lack of light penetration, and dead zones (Kemp et al., 2005). The Chesapeake Bay and tributaries is a well-studied eutrophic system that is plagued with annual dead zones due to increased N inputs from mixed land uses within its watershed (Kemp et al., 2005;Fisher et al., 2006). Conservation practices, such as riparian buffers and wetlands are often used to reduce the water quality impacts of fertilizer. ...
Article
Fertilizer applications on agricultural fields lead to elevated nitrate concentrations in groundwater. This increases nitrate concentrations in the baseflow of streams, enhancing downstream eutrophication. Conservation practices reduce the impacts from agriculture, but little is documented on the recovery time of shallow groundwater after agriculture ceases and conservation practices are applied. Although conservation practices may reduce groundwater nitrate, they may also lead to the production of the greenhouse gas methane. This study investigated the temporal sequence of applying post-agricultural conservation practices and the effects on nitrate and methane concentrations in shallow groundwater. Harleigh Farms is a complex of fields near Oxford, MD (USA) that have been taken out of crop production and placed in conservation programs at various times after 1997. Groundwater nitrate and dissolved methane were sampled monthly from Nov 2012-Nov 2013 using age of the conservation practice as a proxy for time since fertilization. In this chronosequence study, an exponential decline in groundwater nitrate levels was found over the 16 year time period since last fertilization. Within 3–5 years after the cessation of intensive grain production, groundwater nitrate concentrations in the top of the surface unconfined aquifer dropped from 11 mg NO3⁻-N L⁻¹ to 0.5 mg NO3⁻-N L⁻¹. Methane only accumulated to high concentrations (2–60 μM CH4) in hydric soils with low nitrate concentrations (≪ 0.1 mg NO3⁻-N L⁻¹). Our results indicate rapid loss of nitrate in the top of the surficial aquifer after the cessation of intensive agriculture and seasonal accumulations of methane in wetland-based conservation practices. These data indicate that time series of groundwater nitrate concentrations at the top of the unconfined aquifer can be used to evaluate the effectiveness of agricultural conservation practices.
... The Anacostia River runs along the border of Washington D.C. and is highly urbanized and affected by industrial activities and sewage inputs from the city's combined sewer system. The Patuxent watershed is located between Washington D.C. and Baltimore, representing a site of intermediate urban development, and the Choptank River is located across the Chesapeake Bay in Eastern Maryland, where agriculture is the predominant land use [43]. ...
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Urban expansion causes coastal wetland loss, and environmental stressors associated with development can lead to wetland degradation and loss of ecosystem services. This study investigated the effect of urbanization on prokaryotic community composition in tidal freshwater wetlands. Sites in an urban, suburban, and rural setting were located near Buenos Aires, Argentina, and Washington D.C., USA. We sampled soil associated with two pairs of functionally similar plant species, and used Illumina sequencing of the 16S rRNA gene to examine changes in prokaryotic communities. Urban stressors included raw sewage inputs, nutrient pollution, and polycyclic aromatic hydrocarbons. Prokaryotic communities changed along the gradient (nested PerMANOVA, Buenos Aires: p = 0.005; Washington D.C.: p = 0.001), but did not differ between plant species within sites. Indicator taxa included Methanobacteria in rural sites, and nitrifying bacteria in urban sites, and we observed a decrease in methanogens and an increase in ammonia-oxidizers from rural to urban sites. Functional profiles in the Buenos Aires communities showed higher abundance of pathways related to nitrification and xenobiotic degradation in the urban site. These results suggest that changes in prokaryotic taxa across the gradient were due to surrounding stressors, and communities in urban and rural wetlands are likely carrying out different functions.
... The differences in recent N and P trends were strongly related to differences in land use which often reflects both nutrient sources and pollution control efforts. Some of the most successful efforts to reduce nutrient loading have come from improvements to wastewater treatment, combined sewer overflows, and stormwater management in places like Chesapeake Bay (Fisher et al., 2006;Liner et al., 2017;Rice et al., 2017;Sparkman et al., 2017), the Hudson River and Raritan Bay (Hickman and Hirsch, 2017), and in places with tertiary treatment of sewage (Carey and Migliaccio, 2009). The urban watersheds in this study had higher densities of major wastewater facilities than watersheds with other dominant land uses (Fig. S2). ...
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Coastal areas in the U.S. and worldwide have experienced massive population and land-use changes contributing to significant degradation of coastal ecosystems. Excess nutrient pollution causes coastal ecosystem degradation, and both regulatory and management efforts have targeted reducing nutrient and sediment loading to coastal rivers. Decadal trends in flow-normalized nutrient and sediment loads were determined for 95 monitoring locations on 88 U.S. coastal rivers, including tributaries of the Great Lakes, between 2002 and 2012 for nitrogen (N), phosphorus (P), and sediment. N and P loading from urban watersheds generally decreased between 2002 and 2012. In contrast, N and P trends in agricultural watersheds were variable indicating uneven progress in decreasing nutrient loading. Coherent decreases in N loading from agricultural watersheds occurred in the Lake Erie basin, but limited benefit is expected from these changes because P is the primary driver of degradation in the lake. Nutrient loading from undeveloped watersheds was low, but increased between 2002 and 2012, possibly indicating degradation of coastal watersheds that are minimally affected by human activities. Regional differences in trends were evident, with stable nutrient loads from the Mississippi River to the Gulf of Mexico, but commonly decreasing N loads and increasing P loads in Chesapeake Bay. Compared to global rivers, coastal rivers of the conterminous U.S have somewhat lower TN yields and slightly higher TP yields, but similarities exist among land use, nutrient sources, and changes in nutrient loads. Despite widespread decreases in N loading in coastal watersheds, recent N:P ratios remained elevated compared to historic values in many areas. Additional progress in reducing N and P loading to U.S. coastal waters, particularly outside of urban areas, would benefit coastal ecosystems.
... Estuaries are very crucial sites as they act as the bridging zone between a river and oceans and all the anthropogenic loads that fall in the rivers are buffered in these estuarine regions before they enter the sea. Several estuaries are gradually becoming prone to nutrient enrichment and cultural eutrophication (Painting et al. 2007;Wilkerson et al. 2015) due to excessive sewage discharge and fertilizer runoff (Fisher et al. 2006). Similarly, aquaculture ponds are also susceptible to excessive nutrient loading. ...
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The rate of nutrient removal and changes in pCO2 (water) were compared between a lentic aquaculture pond [East Kolkata Wetlands (EKW), India] and a lotic estuarine system [Diamond Harbor (DH) in Hugli Estuary, India] during the post‐monsoon season (experiencing a similar tropical climate) by means of ex situ microcosm experiment. Though the DH waters were found to be substantial source of CO2 towards atmosphere and EKW waters to be sink for CO2 (according to the initial concentration of CO2), the eight consecutive days microcosm experiment revealed that the nutrient removal and pCO2 reduction efficiency were significantly higher in DH (ΔpCO2—90%) compared to EKW (ΔpCO2—78%). Among the five nutrients studied [dissolved nitrate‐nitrogen (NO3–N), dissolved ammonium nitrogen (NH4–N), silicate, phosphate and iron], dissolved NO3–N followed by NH4–N was the most utilized in both EKW and DH. Except silicate, the other nutrients reduced to 78–91% in EKW and 84–99% in DH samples of their initial concentrations. Chlorophyll‐a concentration steadily depleted in EKW (~ 68–26 mg m⁻³) during the experiment indicating intense zooplankton grazing, whereas in DH it increased rapidly (~ 3.4–23 mg m⁻³) with decreasing pCO2 (water). The present observations further indicated that regular flushing of EKW aquaculture ponds is required to avoid stagnation of water column which would enhance the zooplankton grazing and hamper the primary production of an otherwise sink of CO2. In DH, controlled freshwater discharge from Farakka and reduction of untreated organic waste might allow the existing phytoplankton community to enhance their photosynthetic activity.
... Each of these goals is significantly impacted by our global food production system (United Nations, 2015). Maintaining and improving the viability of agriculture is necessary to meet the food demands of the growing global population (Tilman et al., 2002); however, food production significantly contributes to emissions of the greenhouse gas nitrous oxide (N 2 O) leading to global climate change (IPCC, 2016) and to fluxes of nitrate (NO 3 − ) which accelerates water quality decline (e.g., Mitsch et al., 2001;Fisher et al., 2006Fisher et al., , 2010Saaltink et al., 2014). Improved agricultural management is required to reduce the impacts of agriculture on climate change and water quality, while feeding the growing world population. ...
Article
The effects of two agricultural conservation practices on nitrous oxide (N2O) fluxes to the atmosphere and nitrate (NO3⁻) fluxes to groundwater were compared to conventional practices. The conservation practices were application of 80% of recommended nitrogen (N) and planting of winter cover crops. N2O fluxes were measured by static chambers, and NO3⁻ fluxes were calculated using measured NO3⁻ concentrations from tile lines and estimated groundwater yields. During the growing season, one of the five 80% N treatments showed significantly reduced N2O fluxes compared to the 100% N control, whereas three of the five 80% N treatments showed significantly reduced NO3⁻ concentrations compared to the 100% N application. The 80% N treatment resulted in reduced crop yields of 5–26% and average economic losses of US$366 ha⁻¹ for corn and US$153 ha⁻¹ for winter wheat. In three winter cover-crop treatments there were two significant reductions in fall N2O fluxes compared to no-cover-crop controls, and tile drain NO3⁻ concentrations were also significantly lower in autumn. The N2O fluxes were a function of soil temperature, moisture, and fertilizer applications (r² = 0.49, p < 0.001). Integrating N2O and NO3⁻ fluxes to the annual time scale without conservation measures resulted in mean export of 15 ± 8 kg N2O-N ha⁻¹y⁻¹ and 36 ± 6 kg NO3-N ha⁻¹ y⁻¹. Adding an 80% N conservation treatment reduced N2O fluxes by 79% and NO3⁻ fluxes by 22%, whereas adding cover crops had smaller effects (11% for N2O, 9% for NO3⁻). However, cover crops were more cost-effective, averaging US$53 (kg N)⁻¹ compared to the 80% fertilizer treatment (US$77 (kg N)⁻¹) due to large economic losses for corn. The state of Maryland (MD) subsidizes cover crops, making the practice even more cost-effective at US$15 (kg N)⁻¹, emphasizing the importance of farmer-friendly policies.
... Eutrophication due to the increase of anthropogenic nutrients loading, mainly nitrogen and phosphorus, from watersheds has been a central environmental issue along many marine coastal areas over a decade [7]. It causes an increase of phytoplankton biomass and turbidity and decrease of submerged grasses, thus inducing bottom-water hypoxia due to deterioration of excess organic matter [8]. ...
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The discharge of industrial waste water on freshwater resources is on the increase worldwide, including in South Africa. The study aimed at assessing the response of phytoplankton upon exposure to high levels of nutrients along the Tshinane River Limpopo Province. The study showed different phytoplankton assemblages with different changes in physico-chemical levels. Environmental factors do have a noticeable effect on phytoplankton abundance as it was shown by statistical analysis. Results computed by the Czekanowski coefficient showed that various environmental factors components contributed to the different composition and types of phytoplankton abundance (p<0.05). When environmental factors showed fluctuation (Increase or decrease) a different type of plankton was found to be tolerant to those levels. A total of 64 species were identified upstream and 103 species identified downstream. Phytoplankton spectrums were recorded from six taxonomic groups namely Chrysophyta, Dinophyta, Chlorophyta, Bacillariophyta, Cyanophyta and Dinophyta. The dominant taxonomic group was Chlorophyta (Downstream) and Bacillariophyta was the dominant phytoplankton upstream. The results supports the assumption that an increase in nutrients lead to a diverse phytoplankton species even if all the other parameters are within the South African Water Quality Range for Aquatic ecosystems. This shows that tea processing waste has a minimal impact on the ecosystem health of Tshinane River and the river is able to recover from the nutrient enrichment.
... We viewed this additional research as critical because of the urgent need for information on restoration effectiveness (Powledge 2005). The Chesapeake Bay has been in serious ecological decline over the past century (EPA 1982, Kemp et al. 2005) and much of this has been attributed to non-point source runoff that reaches the Bay via the many stream and river tributaries (Boesch et al. 2001, Fisher et al. 2006. Stream restoration and watershed management are integral parts of the Bay restoration program (CBP 2003, CEC 2004, CBP 2005, and, each state within the Bay drainage has been required to develop strategies for improving water quality in its tributaries (CBP 2005). ...
... Chesapeake Bay (Fig. 1) is the largest estuary in the U.S, with an area of 11,601 km 2 and average depth of 7 m. Water quality degradation has become an issue with increased eutrophication (Kemp et al., 2005) due to excessive nutrient loading from freshwater flows (Fisher et al., 2006). Tides are typically below 1 m, and winds and precipitation follow typical dry-and wet-season conditions. ...
Article
Using hyperspectral data collected by the Airborne Compact Atmospheric Mapper (ACAM) and a shipborne radiometer in Chesapeake Bay in July–August 2011, this study investigates diurnal changes of surface remote sensing reflectance (Rrs). Atmospheric correction of ACAM data is performed using the traditional “black pixel” approach through radiative transfer based look-up-tables (LUTs) with non-zero Rrs in the near-infrared (NIR) accounted for by iterations. The ACAM-derived Rrs was firstly evaluated through comparison with Rrs derived from the Moderate Resolution Imaging Spectroradiometer satellite measurements, and then validated against in situ Rrs using a time window of ±1 h or ±3 h. Results suggest that the uncertainties in ACAM-derived Rrs are generally comparable to those from MODIS satellite measurements over coastal waters, and therefore may be used to assess whether Rrs diurnal changes observed by ACAM are realistic (i.e., with changes > 2 × uncertainties). Diurnal changes observed by repeated ACAM measurements reaches up to 66.8% depending on wavelength and location and are consistent with those from the repeated in situ Rrs measurements. These findings suggest that once airborne data are processed using proper algorithms and validated using in situ data, they are suitable for assessing diurnal changes in moderately turbid estuaries such as Chesapeake Bay. The findings also support future geostationary satellite missions that are particularly useful to assess short-term changes.
... The Potomac and the Patuxent estuaries are the first and second most hypoxic of all the sub-estuaries of the Bay. During June-August, 63% of the bottom (sub-pychnocline) water of the Patuxent is hypoxic (Fisher et al. 2006). ...
Article
Watershed land use directly affects the supply of nutrients and sediments to adjacent waters. Higher loads are associated with urban and agricultural land use, often resulting in degraded water quality and increased sedimentation rates. Conservation practices can reduce these loads, but assessing the success of these practices remains challenging. This study evaluates the impacts of land-use conversion from intensive grain agriculture to conservation plantings in Trippe Creek watershed, within the Choptank basin (an estuarine tributary of Chesapeake Bay), compared to those in an adjacent reference watershed (Goldsborough Creek). Changes in both water quality constituents (total nitrogen (N) and phosphorus (P), chlorophyll a) and bottom sediment characteristics (particulate N and P, organic content, grain size) were compared, as well as seasonal- and decadal-scale sedimentation rates using 7Be (half-life 53.3 days) and 210Pb (half-life 22.3 years), respectively. Results provide evidence for improving water quality and reduced sedimentation rates in Trippe Creek, where high concentrations of chlorophyll a decreased to concentrations similar to those in the reference Goldsborough Creek. Sedimentation rates remained fairly steady in Trippe Creek, but increased by ~ 50% in reference Goldsborough Creek. These changes are likely associated with 50% conversion of crop fields to conservation plantings and/or changes in the nature of agriculture over time, offering insight into the effects of land-use change and the difficulties of detecting them in downstream estuarine waters.
Article
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary inputs and watershed conditions. The annual flow‐normalized nitrogen flux to the bay from its watershed declined by 14% to 127,000 Mg (metric tons) between 1992 and 2012, due primarily (more than 80% of the decline) to reduced point sources. The remainder of the decline was due to reduced atmospheric deposition (13%) and urban nonpoint sources. Agricultural inputs, which contribute most nitrogen to the bay, changed little, although trends in the average nitrogen yield (flux per unit area) from cropland and pasture to streams in some settings suggest possible effects of evolving nutrient applications or other land management practices. Point sources of phosphorus to local streams declined by half between 1992 and 2012, while nonpoint inputs were relatively unchanged. Annual phosphorus delivery to the bay increased by 9% to 9,570 Mg between 1992 and 2012, however, due mainly to reduced retention in the Susquehanna River at Conowingo Reservoir. Research Impact Statement: Point‐source reductions account for more than 80% of the decline in nitrogen flux to Chesapeake Bay between 1992 and 2012, but were offset by rising phosphorus inputs from the Susquehanna River.
Article
Water security is a top concern for social well-being, and dramatic changes in the availability of freshwater have occurred as a result of human uses and landscape management. Elevated nutrient loading and perturbations to major ion composition have resulted from human activities and have degraded freshwater resources. This study addresses the emerging nature of streamwater quality in the 21st century through analysis of concentrations and trends in a wide variety of constituents in streams and rivers of the U.S. Concentrations of 15 water quality constituents including nutrients, major ions, sediment, and specific conductance were analyzed over the period 1982-2012 and a targeted trend analysis was performed from 1992 to 2012. Although environmental policy is geared toward addressing the long-standing problem of nutrient overenrichment, these efforts have had uneven success, with decreasing nutrient concentrations at urbanized sites and little to no change at agricultural sites. Additionally, freshwaters are being salinized rapidly in all human-dominated land use types. While efforts to control nutrients are ongoing, rapid salinity increases are ushering in a new set of poorly defined issues. Increasing salinity negatively affects biodiversity, mobilizes sediment-bound contaminants, and increases lead contamination of drinking water, but its effects are not well integrated into current paradigms of water management.
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During recent decades, environmental conditions have deteriorated in the Black Sea. Population explosions of phytoplankton and jellyfish have become frequent and several fish stocks have collapsed. In this study, literature sources and long-term data are explored in order to find empirical evidence for ecosystem effects of fishing. Inverse trends of decreasing predators, increasing planktivorous fish, decreasing zooplankton and increasing phytoplankton biomass are revealed. Increased phytoplankton biomass provoked decreasing transparency and nutrient content in surface water, A massive development of jellyfish during the 1970s and 1980s had a great impact on consumption and consequent decrease in zooplankton. The turning point for these changes occurred in the early 1970s, when industrial fishing started and stocks of pelagic predators (bonito, mackerel, bluefish, dolphins) became severely depleted. A 'trophic cascade' is, invoked as a mechanism to explain observed changes. According to this hypothesis, reduction in apex predators decreases consumer control and leads to higher abundance of planktivorous fish. The increased consumption by planktivorous fish causes a consequent decline in zooplankton biomass, which reduces grazing pressure on phytoplankton and allows its standing crop to increase. The effects of fishing and eutrophication are explored using a dynamic mass-balance model, A balanced model is built using 15 ecological groups including bacteria, phytoplankton, zooplankton, protozoa, ctenophores, medusae, chaetognaths, fishes and dolphins. Ecosystem dynamics are simulated over 30 yr, assuming alternative scenarios of increasing fishing pressure and eutrophication, The changes in simulated biomass are similar in direction and magnitude to observed data from long-term monitoring. The cascade pattern is explained by the removal of predators and its effect on trophic interactions, while the inclusion of eutrophication effects leads to biomass increase in all groups. The present study demonstrates that the combination of uncontrolled fisheries and eutrophication can cause important alterations in the structure and dynamics of a large marine ecosystem. These findings may provide insights for ecosystem management, suggesting that conserving and restoring natural stocks of fish and marine mammals can contribute greatly to sustaining viable marine ecosystems.
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Using shipboard bioassays, we examined the roles rainfall, individual and combined nutrients play in accelerating primary production in coastal, Gulf Stream and pelagic (Sargasso Sea) locations in the North Atlantic Ocean off North Carolina, USA, from 1993 to 1995. Photosynthetic CO2 fixation and net chlorophyll a (chl a) production were measured in replicated bioassays to assess individual and combined impacts of different constituents of atmospheric deposition, including natural rainfall, a synthetic rain mix, dissolved inorganic nitrogen (DIN; NH4+, NO3-), dissolved organic nitrogen (DON; urea), phosphorus (PO43-) and iron (as EDTA-chelated and unchelated FeCl3). Natural rainfall and DIN additions most often stimulated CO2 fixation and chi a production, but frequencies and magnitudes of biostimulation, relative to controls. varied between these indicators. Spatial differences in the types and magnitudes of stimulation were also observed. When added in equimolar amounts, NH4+ was, at times, more stimulatory than NO3-. The NO3- stimulation was significantly enhanced by Fe-EDTA. Urea was marginally stimulatory at the coastal location. PO43- was never stimulatory. Fe-EDTA and EDTA by themselves stimulated production only at the offshore locations, suggesting increased Fe limitation with increasing distance from land. Synthetic rain, which contained both sources of DIN, but not Fe, generally proved less stimulatory per unit N than natural rainfall. Results indicate a broad sensitivity of these waters to N additions, which in the case of NO3- are enhanced by Fe-EDTA. At all locations, the high level of stimulation of primary production attributable to natural rain may be due to the supply of both DIN and co-limiting nutrients (e.g. Fe), contributing to the eutrophication potential of waters downwind of urban, industrial and agricultural emissions.
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During a 1-year period we measured discharges of water, suspended solids, and nutrients from 27 watersheds having differing proportions of cropland in the Piedmont and Coastal Plain provinces of the Chesapeake Bay drainage. Annual flow-weighted mean concentrations of nitrate and organic N and C in stream water correlated with the relative proportions of base flow and storm flow. As the proportion of base flow increased, the concentration of nitrate increased and the concentrations of organic N and C decreased. This suggests that discharge of nitrate is promoted by groundwater flow but discharges of organic N and C are promoted by surface runoff. Concentrations of N species also increased as the proportion of cropland increased. We developed a statistical model that predicts concentrations of N species from the proportions of cropland and base flow. P concentrations did not correlate with cropland or base flow but correlated with the concentration of suspended solids, which differed among watersheds.
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The importance of P originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well-known role of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long-term overfertilization and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestern USA (Indiana), and eastern Canada (Quebec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in subsurface runoff.
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The history and fate of groundwater nitrate (NO3-) contamination were compared in 2 small adjacent agricultural watersheds in the Atlantic coastal plain by combined use of chronologic (CCl2F2, 3H), chemical (dissolved solids, gases), and isotopic (δ15N, δ13C, δ34S) analyses of recharging groundwaters, discharging groundwaters, and surface waters. The results demonstrate the interactive effects of changing agricultural practices, groundwater residence times, and local geologic features on the transfer of NO3- through local flow systems. -from Authors
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A primary focus of coastal science during the past 3 decades has been the question: How does anthropogenic nutrient enrichment cause change in the structure or function of nearshore coastal ecosystems? This theme of environmental science is recent, so our conceptual model of the coastal eutrophication problem continues to change rapidly. In this review, I suggest that the early (Phase I) conceptual model was strongly influenced by limnologists, who began intense study of lake eutrophication by the 1960s. The Phase I model emphasized changing nutrient input as a signal, and responses to that signal as increased phytoplankton biomass and primary production, decomposition of phytoplankton-derived organic matter, and enhanced depletion of oxygen from bottom waters. Coastal research in recent decades has identified key differences in the responses of lakes and coastal-estuarine ecosystems to nutrient enrichment. The contemporary (Phase II) conceptual model reflects those differences and includes explicit recognition of (1) system-specific attributes that act as a filter to modulate the responses to enrichment (leading to large differences among estuarine-coastal systems in their sensitivity to nutrient enrichment); and (2) a complex suite of direct and indirect responses including linked changes in: water transparency, distribution of vascular plants and biomass of macroalgae, sediment biogeochemistry and nutrient cycling, nutrient ratios and their regulation of phytoplankton community composition, frequency of toxic/harmful algal blooms, habitat quality for metazoans, reproduction/growth/survival of pelagic and benthic invertebrates, and subtle changes such as shifts in the seasonality of ecosystem functions. Each aspect of the Phase II model is illustrated here with examples from coastal ecosystems around the world. In the last section of this review I present one vision of the next (Phase III) stage in the evolution of our conceptual model, organized around 5 questions that will guide coastal science in the early 21st century: (1) How do system-specific attributes constrain or amplify the responses of coastal ecosystems to nutrient enrichment? (2) How does nutrient enrichment interact with other stressors (toxic contaminants, fishing harvest, aquaculture, nonindigenous species; habitat loss, climate change, hydrologic manipulations) to change coastal ecosystems? (3) How are responses to multiple stressors linked? (4) How does human-induced change in the coastal zone impact the Earth system as habitat for humanity and other species? (5) How can a deeper scientific understanding of the coastal eutrophication problem be applied to develop tools for building strategies at ecosystem restoration or rehabilitation?
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The loss of submerged aquatic vegetation (SAV) from the Patuxent estuary during the latter part of the 20th century was explored using diverse data sets that included historic SAV coverage and distribution data, SAV ground truth observations, water clarity and nutrient loading data, and epiphyte light attenuation measurements. Analysis of aerial photography from 1952 showed that SAV was abundant and widely distributed along the entire mesohaline region of the estuary; by the late 1960s rapid declines in SAV took place following large increases in nutrient loading to the estuary. An examination of water clarity and epiphyte data suggest that the processes that led to the loss of SAV varied in strength along the axis of the estuary. In the upper mesohaline region, Secchi depths were consistently less than established mesohaline SAV habitat requirements at 1-m water depth, suggesting that water clarity was responsible for SAV decline. In the lower mesohaline region, where water clarity was consistently above SAV requirements, high epiphyte fouling rates significantly reduced light available to SAV. Experimental results show that epiphyte fouling had the capacity to reduce available light to SAV blades from 30% to 7% of surface light within a week, and likely contributed to the local decline and near total loss of SAV during the late 1960s and early 1970s. The prognosis for near-term SAV recovery within the mesohaline portion of the estuary seems unlikely given existing water quality conditions.
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We used the hydrochemical model GWLF to estimate terrestrial diffuse fluxes from ungauged areas of a coastal plain catchment, the Choptank River basin. The gauged area of the basin is 17% of the land surface, and we divided the remaining ungauged area into 21 subbasins. Three comparative approaches were used: (1) application of area yield coefficients based on 11 years of observations from the gauged area to extrapolate over ungauged subbasins without modeling, (2) application of GWLF to estimate export from all subbasins using model parameters calibrated in the gauged subbasin, and (3) application of GWLF with parameter adjustments based on the local characteristics in each subbasin. Comparison of the predicted export from 6 selected subbasins with observed export data showed that application of GWLF with local adjustments reduced model errors of N export from 43% to 27%. With only one adjustment for sediment P, application of GWLF alone reduced errors of P export from 92%to 40–45%, with or without local adjustments for flow and sediment retention. The data supported the hypothesis that significant spatial variations in N and P yields introduce large errors when extrapolating from gauged to ungauged subbasins, and estimated TN and TP yield coefficients varied over 1–21 kg N and 0.1–0.5 kg P ha–1 y–1 in ungauged areas due to varying human population densities, soil drainage characteristics, and amounts of agriculture. The most accurate estimates of terrestrial diffuse sources were combined with point source discharges and wet atmospheric inputs to estimate annual average inputs of 2.5 106 kg N and 5.8 104 kg P y–1 to the Choptank estuary during 1980–1996. These results illustrate the problems of spatial extrapolation from gauged to ungauged areas and emphasize the need for application of local characteristics for accurate assessment of watershed export.
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We report nutrient addition bioassays at 18 stations in Chesapeake Bay (USA) to assess resources limiting phytoplankton growth. Data were pooled from several sampling programs conducted from 1989 to 1994. Spatially, light and P limitation declined from low salinity regions to high salinity regions, as N limitation increased. This spatial pattern was driven primarily by freshwater inflows with high N/P and seawater inflows with low N/P. Seasonally, there was a marked progression of winter light limitation, spring P limitation, and summer N limitation at mesohaline and polyhaline stations. The seasonal pattern appeared to be caused by temperature, mixing, river discharge, and sediment P fluxes. At high salinity stations, we also observed winter N limitation (caused by DIN depletion prior to spring nitrate delivery), and at lower salinity stations there was fall P limitation (caused by reaeration of bottom sediments). At tidal fresh stations, turbidity and nutrient concentrations resulted in continuous light limitation, except at some stations in summer. Interannual decreases in light limitation and increases in N and P limitation appear to represent improvements in water quality.
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In this paper we assemble and analyze quantitative annual input-export budgets for total nitrogen (TN) and total phosphorus (TP) for Chesapeake Bay and three of its tributary estuaries (Potomac, Patuxent, and Choptank rivers). The budgets include estimates of TN and TP sources (point, diffuse, and atmospheric), internal losses (burial in sediments, fisheries yields, and denitrification), storages in the water column and sediments, internal cycling rates (zooplankton excretion and net sediment-water flux), and net downstream exchange. Annual terrestrial and atmospheric inputs (average of 1985 and 1986 data) of TN and TP ranged from 4.3 g TN m−2 yr−1 to 29.3 g TN m−2 yr−1 and 0.32 g TP m−2 yr−1 to 2.42 g TP m−2 yr−1, respectively. These rates of TN and TP input represent 6-fold to 8-fold and 13-fold to 24-fold increases in loads to these systems since the precolonial period. A recent 11-yr record for the Susquehanna River indicates that annual loads of TN and TP have varied by about 2-fold and 4-fold, respectively. TN inputs increased and TP inputs decreased during the 11-yr period. The relative importance of nutrient sources varied among these estuaries: point sources of nutrients delivered about half the annual TN and TP load to the Patuxent and nearly 60% of TP inputs to the Choptank; diffuse sources contributed 60–70% of the TN and TP inputs to the mainstream Chesapeake and Potomac River. The direct deposition of atmospheric wet-fall to the surface waters of these estuaries represented 12% or less of annual TN and TP loads except in the Choptank River (37% of TN and 20% of TP). We found direct, although damped, relationships between annual rates of nutrient input, water-column and sediment nutrient stocks, and nutrient losses via burial in sediments and denitrification. Our budgets indicate that the annual mass balance of TN and TP is maintained by a net landward exchange of TP and, with one exception (Choptank River), a net seaward transport of TN. The budgets for all systems revealed that inorganic nutrients entering these estuaries from terrestrial and atmospheric sources are rapidly converted to particulate and organic forms. Discrepancies between our budgets and others in the literature were resolved by the inclusion of sediments derived from shoreline erosion. The greatest potential for errors in our budgets can be attributed to the absence of or uncertainties in estimates of atmospheric dry-fall, contributions of nutrients via groundwater, and the sedimentation rates used to calculate nutrient burial rates.
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A 52-yr record of dissolved oxygen in Chesapeake Bay (1950–2001) and a record of nitrate (NO3 −) loading by the Susquehanna River spanning a longer period (1903, 1945–2001) were assembled to describe the long-term pattern of hypoxia and anoxia in Chesapeake Bay and its relationship to NO3 − loading. The effect of freshwater inflow on NO3 − loading and hypoxia was also examined to characterize its effect at internannual and longer time scales. Year to year variability in river flow accounted for some of the observed changes in hypoxic volume, but the long-term increase was not due to increased river flow. From 1950–2001, the volume of hypoxic water in mid summer increased substantially and at an accelerating rate. Predicted anoxic volume (DO<0.2 mg I−1) at average river flow increased from zero in 1950 to 3.6×109 m3 in 2001. Severe hypoxia (DO<1.0 mg I−1) increased from 1.6×109 to 6.5×109 m3 over the same period, while mild hypoxia (DO<2.0 mg I−1) increased from 3.4×109 to 9.2×109 m3. NO3 − concentrations in the Susquehanna River at Harrisburg, Pennsylvania, increased up to 3-fold from 1945 to a 1989 maximum and declined through 2001. On a decadal average basis, the superposition of changes in river flow on the long-term increase in NO3 − resulted in a 2-fold increase in NO3 − loading from the Susquehanna River during the 1960s to 1970s. Decadal average loads were subsequently stable through the 1990s. Hypoxia was positively correlated with NO3 − loading, but more extensive hypoxia was observed in recent years than would be expected from the observed relationship. The results suggested that the Bay may have become more susceptible to NO3 − loading. To eliminate or greatly reduce anoxia will require reducing average annual total nitrogen loading to the Maryland mainstem Bay to 50×106 kg yr−1, a reduction of 40% from recent levels.
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Nutrient over-enrichment and cultural eutrophication are significant problems in the Danish marine environment. Symptoms of eutrophication include periods of hypoxia and anoxia in bottom waters, death of benthic-dwelling organisms during anoxia, long-term reductions in the depth distribution of macrophyte communities, changes in the species composition of macrophyte communities, and increases in reports of harmful algal blooms. In 1987 the Action Plan on the Aquatic Environment was adopted to combat nutrient pollution of the aquatic environment with the overall goal of reducing nitrogen loads by 50% and point source phosphorus loads by 80%. The Danish Aquatic Nation-wide Monitoring Program was begun in 1988 in order to describe the status of point sources (industry, sewage treatment plants, stormwater outfalls, scattered dwellings, and fish farms), ground water, springs, agricultural watersheds, streams, lakes, atmospheric deposition, and the marine environment. Another important aspect of the program was to document the effects on the aquatic environment of the measures and investments taken for nutrient reduction as outlined in the Action Plan. The monitoring program should determine if reductions in nutrients are achieved by the measures taken and should help decision makers choose appropriate additional measures to fulfill the objectives. Coordination with international programs and commissions is an important component of the monitoring program to meet internationally agreed upon reductions in nutrient inputs. The future and direction of the Danish National Aquatic Monitoring and Assessment Program will be to a large extent shaped by both the Water Framework Directive and Habitat Directive adopted by the European Union.
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The Patuxent River, Maryland, is a nutrient-overenriched tributary of the Chesapeake Bay. Nutrient inputs from sewage outfalls and nonpoint sources (NPS) have grown substantially during the last four decades, and chlorophylla levels have increased markedly with concomitant reductions in water quality and dissolved oxygen concentrations. The Patuxent has gained national attention because it was one of the first river basins in the U.S. for which basin-wide nutrient control standards were developed. These included a reduction in NPS inputs and a limit on both nitrogen (N) and phosphorus (P) loadings in sewage discharges intended to return the river to 1950s conditions. Full implementation of point source controls occurred by 1994, but population growth and land-use changes continue to increase total nutrient loadings to the river. The present paper provides the perspectives of scientists who participated in studies of the Patuxent River and its estuary over the last three decades, and who interacted with policy makers as decisions were made to develop a dual nutrient control strategy. Although nutrient control measures have not yet resulted in dramatic increases in water quality, we believe that without them, more extensive declines in water quality would have occurred. Future reductions will have to come from more effective NPS controls since future point source loading will be difficult to further reduce with present technology. Changing land use will present a challenge to policy makers faced with sprawling population growth and accelerated deforestation.
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Land-cover changes in the Choptank basin were estimated for 1665–1820 by using historical socioeconomic data and crop-rotation models. Socioeconomic data (human population, output per laborer, and crop yields) were obtained from the literature, whereas crop-rotation models, based on historical records, represented how agriculture was practiced. Model parameters and output were validated with export records, census data, and other historical records, and model errors were estimated to be approximately 5%. This approach indicated a sigmoidal pattern for conversion of primary forest to agricultural land by 1800. The initial time period, 1665–1720, was characterized by low-intensity tobacco and corn cultivation. Due to long fallows, the models indicated that there was little land in crops (approximately 5% of the region), but larger areas of secondary forest occurred on former cropland (approximately 15%). Although primary forest decreased, the initial result in the first 55 years was a low net rate of deforestation and occupation by low-intensity farms. However, after 1720, cropland expanded rapidly due to the use of wheat as a cash crop. From 1720 to 1775, primary and secondary forest rapidly disappeared, increasing agricultural land to 60% of the region. By 1800, approximately 80% was estimated to be converted to agriculture, and little primary forest remained. After 1800, the land needed for crops decreased due to improved management practices and crop yields, and some secondary forest on formerly cleared agricultural sites may have reappeared. We estimate that less than 150 years of European colonization resulted in virtually complete agriculturalization of a primarily forested landscape.
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We developed an empirical model integrating nonpoint source (NPS) runoff, point sources (PS), and reservoir management to predict watershed discharges of water, sediment, organic carbon, silicate, nitrogen, and phosphorus to the Patuxent River in Maryland. We estimated NPS discharges with linear models fit to measurements of weekly flow and 10 material concentrations from 22 study watersheds. The independent variables were the proportions of cropland and developed land, physiographic province (Coastal Plain or Piedmont), and time (week). All but one of the NPS models explained between 62% and 83% of the variability among concentration or flow measurements. Geographic factors (land cover and physiographic province) accounted for the explained variability in largely dissolved material concentrations (nitrate [NO3], silicate [Si], and total nitrogen [TN]), but the explained variability in flow and particulates (sediment and forms of phosphorus) was more strongly related to temporal variability or its interactions with land cover and province. Average concentrations of all materials increased with cropland proportion and also with developed land (except Si), but changes in cropland produced larger concentration shifts than equivalent changes in developed land proportion. Among land cover transitions, conversions between cropland and forest-grassland cause the greatest changes in material discharges, cropland and developed land conversions are intermediate, and developed land and forest-grassland conversions have the weakest effects. Changing land cover has stronger effects on NO3 and TN in the Piedmont than in the coastal Plain, but for all other materials, the effects of land-use change are greater in the Coastal Plain. We predicted the changes in nutrient load to the estuary under several alternate land cover configurations, including a state planning scenario that extrapolates current patterns of population growth and land development to the year 2020. In that scenario, declines in NPS discharges from reducing cropland are balanced by NPS discharge increases from developing an area almost six times larger than the lost cropland. When PS discharges are included, there are net increases in total water, total phosphorus, and TN discharges.
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We quantified annual nutrient inputs to the Patuxent River estuary from point and nonpoint sources and from direct atmospheric deposition. We also compared nonpoint source (NPS) discharges from Piedmont and Coastal Plain regions and from agricultural and developed lands. Using continuous automated-sampling, we measured discharges of water, nitrogen, phosphorus, organic carbon (C), and suspended solids from a total of 23 watersheds selected to represent various proportions of developed land and cropland in the Patuxent River basin and the neighboring Rhode River basin. The sampling period spanned two years that differed in annual precipitation by a factor of 1.7. Water discharge from the watershed to the Patuxent River estuary was 3.4 times higher in the wet year than in the dry year. Annual water discharges from the study watersheds increased as the proportion of developed land increased. As the proportion of cropland increased, there were increases in the annual flow-weighted mean concentrations of nitrate (NO3-), total nitrogen (TN), dissolved silicate (Si), total phosphate (TPO43-), total organic phosphorus (TOP), total P (TP), and total suspended solids (TSS) in NPS discharges. The effect of cropland on the concentrations of NO3- and TN was stronger for Piedmont watersheds than for Coastal Plain watersheds. As the proportion of developed land increased, there were increases in annual mean concentrations of NO3-, total ammonium (TNH4+), total organic N (TON), TN, total organic C (TOC), TPO43-, TOP, TP, and TSS and decreases in concentrations of Si. Annual mean concentrations of TON, TOC, forms of P, and TSS were highest in the wet year. Annual mean concentrations of NO3-, TNH4+, TN, and Si did not differ significantly between years. We directly measured NPS discharges from about half of the Patuxent River basin and estimated discharges from the other half of the basin using statistical models that related annual water flow and material concentrations to land cover and physiographic province. We compared NPS discharges to public data on point source (PS) discharges. We estimated direct atmospheric deposition of forms of N, P, and organic C to the Patuxent River estuary based on analysis of bulk deposition near the Rhode River. During the wet year, most of the total terrestrial and atmospheric inputs of forms of N and P came from NPS discharges. During the dry year, 53% of the TNH4+ input was from atmospheric deposition and 58% of the NO3- input was from PS discharges; NPS and PS discharges were about equally important in the total inputs of TN and TPO43-. During the entire 2-yr period, the Coastal Plain portion of the Patuxent basin delivered about 80% of the NPS water discharges to the estuary and delivered similar proportions of the NPS TNH4+, TN, TOP, and TSS. The Coastal Plain delivered greater proportions of the NPS TON, TOC, Si, and TP (89%, 90%, 93%, and 95%, respecfively) than of water, and supplied nearly all of the NPS TPO43- (99%). The Piedmont delivered 33% of the NPS NO3- while delivering only 20% of the NPS water to the estuary. We used statistical models to infer the percentages of NPS discharges supplied by croplands, developed lands, and other lands. Although cropland covers only 10% of the Patuxent River basin, it was the most important source of most materials in NPS discharge, supplying about 84% of the total NPS discharge of NO3-; about three quarters of the TPO43-, TOP, TP, and TSS; and about half of the TNH4+ and TN. Compared to developed land, cropland supplied a significantly higher percentage of the NPS discharges of NO3-, TN, TPO43-, TOP, TP, and TSS, despite the fact developed land covered 12% of the basin.
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Nutrient transformation and phytoplankton growth were examined in 9 river-dominated sub-tropical east Australian estuaries in 1996 using modified mixing diagrams. The sampling program was rapid and strictly controlled, using 2 or 3 boats simultaneously, so that all 9 estuaries were usually sampled within 4 to 5 d of each other. River samples were collected at the head of each estuary on a flow-weighted basis, and variations in river concentrations and flushing times were used to calculate conservative mixing lines. This was to avoid ‘apparent’ non-linear distributions in the mixing diagrams associated with river-source variations on a time scale less or equal to the flushing time of the estuary. A number of general patterns of biogeochemical behaviour were observed across most, or all, of the estuaries. The 4 northern, and most likely the 5 southern, estuaries flushed fresh to the mouth during a flood in May, allowing most of the flood-borne material to escape from the system. Phytoplankton appear to exert the dominant control on nutrient transformation in the 9 estuaries, with non-biological processes only playing a minor role, if any. Eight of the 9 estuaries are potentially nutrient-limited, with nutrient concentrations falling below the upper half-saturation constants required for phytoplankton growth. The estuaries became potentially more P-limited, and less N-limited, as the wastewater loading to each system increased. During most sampling runs, maximum and mean concentrations of phytoplankton biomass chlorophyll a) in the Tweed, Brunswick, Bellinger, Nambucca, Macleay and Hastings estuaries were significantly correlated with the wastewater DIN (dissolved inorganic nitrogen) loading index (daily wastewater load per m 3 of estuary volume multiplied by the flushing time of the estuary in days). In contrast, the diffuse DIN loading index appeared more important for controlling phytoplankton biomass (chlorophyll a) in the 3 estuaries (Richmond, Clarence and Manning) that received a low wastewater DIN load. Sub-tropical Australian estuaries are characterised by a high degree of variability in nutrient delivery and phytoplankton growth. The timing and magnitude of hydrological factors appears to be the major feature that determines the differences in the temporal patterns of phytoplankton growth between sub-tropical and temperate regions. Nutrient-loading and phytoplankton growth in the 9 estuaries appears to be in phase, suggesting that stored and recycled nutrients may play a smaller role in maintaining phytoplankton growth in these systems compared to the larger partially mixed temperate systems. Management efforts in the 9 estuaries should be first directed towards reducing the wastewater DIN loading index to <1, followed by management strategies focused on controlling diffuse loadings. There may, however, be a trade-off associated with reducing the wastewater loading index with a proportional reduction in fisheries production.
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Nitrate contamination of shallow groundwater has been widely documented in association with agriculture in the Coastal Plain region of the Chesapeake Bay watershed. Elevated groundwater nitrate levels limit the use of shallow groundwater for human consumption and also result in elevated nonpoint source nitrogen (N) loads to Chesapeake Bay via elevated stream base-flow nitrate concentrations. This study investigated the effects of cereal grain winter cover crops on nitrate leaching rates, profile nitrate storage, and nitrate concentrations in shallow groundwater in two field-scale watersheds planted continuously in corn (Zea mays L.) from 1984 through 1996. Winter-fallow conditions were maintained following the 1984 through 1987 growing seasons and cereal rye (Secale cereale L.) as a cover crop was planted immediately after grain harvest from 1988 through 1996. Cover crop effects on nitrate leaching rates also were evaluated in continuous no-till corn plots from 1990 through 1995. Nitrate leaching losses from the root zone and recharge of shallow aquifers occurred primarily during winter months under conditions of low evapotranspiration. The potential for nitrate leaching losses was determined primarily by the availability of nitrate in the root zone at the onset of the winter groundwater recharge period. Rye winter cover crops planted after corn harvest consistently reduced nitrate-N concentrations in root zone leachate to less than 1 mg/L during most of the groundwater recharge period, and reduced annual nitrate leaching losses by approximately 80% relative to winter-fallow treatments. Shallow groundwater nitrate-N concentrations under long-term continuous corn production decreased from the 10 to 20 mg/L range to less than 5 mg/L after seven years of cover crop use. Cover crops appeared to increase corn yields under adverse growing season conditions, but limited residual nitrate availability during the growing season relative to winter-fallow settings. Cover crop growth was generally N limited, suggesting that increased N inputs would have little effect on nitrate leaching, but would increase cover crop contributions to soil carbon pools.
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There is a need in the marine research and management communities for a clear operational definition of the term, eutrophication. I propose the following: eutrophication (noun) - an increase in the rate of supply of organic matter to an ecosystem. This definition is consistent with historical usage and emphasizes that eutrophication is a process, not a trophic state. A simple trophic classification for marine systems is also proposed: [GRAPHICS] Various factors may increase the supply of organic matter to coastal systems, but the most common is clearly nutrient enrichment. The major causes of nutrient enrichment in coastal areas are associated directly or indirectly with meeting the requirements and desires of human nutrition and diet. The deposition of reactive nitrogen emitted to the atmosphere as a consequence of fossil fuel combustion is also an important anthropogenic factor. The intensity of nitrogen emission from fertilizer, livestock waste, and fossil fuel combustion varies widely among the countries of the world. It is strongest in Europe, the northeastern United States, India/Pakistan, Japan/Korea, and the Caribbean. This geographical distribution corresponds with many areas where coastal marine eutrophication has become a recent concern. Demographic and social trends suggest that past practices leading to coastal nutrient enrichment are likely to be repeated in the coming decades in the developing countries of Asia, Africa, and Latin America.
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Phosphate concentrations in rainwater were measured at a Ligurian coastal sampling site (Cap Ferrat, France) from February 1997 to February 1998 to study the impact of wet atmospheric phosphorus (P) input on the surface ocean. Soluble and particulate fractions were differentiated to evaluate the atmospheric supply of bioavailable P. Complexed and reactive phases within the dissolved fraction were also separated. Preliminary results showed a high temporal variability in total concentration (0.05-4.3 μmol liter-1). The factors controlling the partitioning between reactive and complexed components are not clear. However, the partitioning between dissolved and particulate fractions is linked to emission sources. Soil-derived dust from the Sahara was identified as an important source of atmospheric P, mainly insoluble. Conversely, anthropogenic emissions are sources of soluble P (i.e., basically bioavailable). A significant part of these emissions could originate from incinerators and/or biomass burning. The different wet fluxes are calculated to total 165 μmol m-2 yr-1, and the dissolved and particulate inputs are 95 and 70 μmol m-2 yr-1, respectively. Taking into account the respective solubility of such inputs, anthropogenic emissions appear to be responsible for relatively high amounts of bioavailable P. Even if the atmosphere is globally a minor source of nutrients (compared with riverine inputs and marine vertical mixing), it might be the only source of P in oligotrophic conditions. For example, assuming that P is a limiting factor in the Mediterranean Sea, the rain event of 19 June 1997 (17 μmol m-2 of bioavailable P) potentially induced a new production of 0.02 g C m-2, which is a significant value in such conditions. Converted into biomass and integrated over a 5-m-thick water layer, such an atmospheric input represents 0.35-0.45 mg chlorophyll a m-2, an appreciable portion of the total biomass during this period. This observation underlines the major role of the atmosphere during oligotrophic periods in the western Mediterranean.
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Nitrogen is a key element controlling the species composition, diversity, dynamics, and functioning of many terrestrial, freshwater, and marine ecosystems. Many of the original plant species living in these ecosystems are adapted to, and function optimally in, soils and solutions with low levels of available nitrogen. The growth and dynamics of herbivore populations, and ultimately those of their predators, also are affected by N. Agriculture, combustion of fossil fuels, and other human activities have altered the global cycle of N substantially, generally increasing both the availability and the mobility of N over large regions of Earth. The mobility of N means that while most deliberate applications of N occur locally, their influence spreads regionally and even globally, Moreover, many of the mobile forms of N themselves have environmental consequences. Although most nitrogen inputs serve human needs such as agricultural production, their environmental consequences are serious and long term. Based on our review of available scientific evidence, we are certain that human alterations of the nitrogen cycle have: 1) approximately doubled the rate of nitrogen input into the terrestrial nitrogen cycle, with these rates still increasing; 2) increased concentrations of the potent greenhouse gas N2O globally, and increased concentrations of other oxides of nitrogen that drive the formation of photochemical smog over large regions of Earth; 3) caused losses of soil nutrients, such as calcium and potassium, that are essential for the long-term maintenance of soil fertility; 4) contributed substantially to the acidification of soils, streams, and lakes in several regions; and 5) greatly increased the transfer of nitrogen through rivers to estuaries and coastal oceans. In addition, based on our review of available scientific evidence we are confident that human alterations of the nitrogen cycle have: 6) increased the quantity of organic carbon stored within terrestrial ecosystems; 7) accelerated losses of biological diversity, especially losses of plants adapted to efficient use of nitrogen, and losses of the animals and microorganisms that depend on them; and 8) caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.
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Fisheries of enclosed and semi‐enclosed seas provide the first basis for evaluating human impacts on marine ecosystems. These have become of serious concern before similar changes are detectable in oceanic systems, thus emphasizing their value as laboratories for comparative study of man‐induced changes. The paper discusses the relevance of the cline, oligo‐meso‐eu‐dys‐trophic to stressed marine systems, and focuses on impacts on fisheries of enhanced nutrient runoff, noting common features with marine systems subject to natural enrichment, but also with well‐studied freshwater systems. It is suggested that under nutrient enrichment and heavy fishing, both “top down”; and “bottom up”; trophic mechanisms act in synchrony to change the trophic chain, leading initially to increased fishery productivity of formerly oligotrophic systems, followed by more drastic and negative changes as nutrient input passes beyond a state that may be called mesotrophic.
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Moored measurements and hydrographic surveys were carried out during the summers of 1986 and 1987 to examine interaction between the mainstem of the Chesapeake Bay and the Choptank River, an eastern shore tributary estuary. The data show that an important mode of interaction is through wind-forced intrusion of saline, hypoxic water from below the pycnocline of the Bay into the lower river. Intrusions are driven by lateral tilting of the pycnocline in the Bay, when high salinity water is upwelled on the eastern side of the Bay in response to a southward pulse of wind stress. The resulting internal surges propagate up the relict Choptank entrance channel at a speed of about 20 cm/s and spill onto the broad sill inside the mouth of the river. Intrusion-favorable pycnocline tilts in the Bay do not always result in lower layer intrusion into the Choptank, but may be blocked or choked in the entrance channel on occasion. The data suggest that wind-forced intrusion of salt leads to increased gravitational circulation in the Choptank during the summer months, providing a mechanism through which high frequency energy may be directly translated into lower frequency motion.
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Near-shore, shallow waters in the Chesapeake Bay periodically experience episodes of anoxia or severe hypoxia during summer. In order to examine the severity and temporal pattern of hypoxia, and environmental factors that may lead to such episodes, dissolved oxygen, salinity and temperature were measured at 15-min intervals during the summers of 1987 and 1988 in a western shore oyster bed. Bottom dissolved oxygen concentrations averaged lower at a 4-m site than at a 2-m site. At the 4-m site, dissolved oxygen concentrations dropped below 2 mg l−1 during approximately 40% of days and below 1 mg l−1 during approximately 10% of days each summer. However, diel fluctuations in oxygen concentrations were sufficiently large that even on days of the most severe oxygen minima, dissolved oxygen concentrations always reached or exceeded a level tolerable by most estuarine organisms during some part of the day.
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Fluxes of dissolved nitrogen (N) as nitrate from forested watersheds in the mid-Appalachian region have important water quality ramifications for small acid-sensitive streams and for downstream receiving waters such as the Chesapeake Bay. Previous studies of N leakage have suggested that annual dissolved N fluxes from small watersheds can vary by several orders of magnitude and may be increasing as second-growth forests gradually become N saturated from the accrual of atmospheric N loadings. In this study, we examined the temporal (intra-annual and interannual) variability in dissolved nitrate fluxes from five small (area < 15 km2) forested watersheds in the mid-Appalachian region from 1988 to 1995. At all sites, nitrate concentrations were observed to increase dramatically during storm flow events, with nitric acid contributing significantly to depressions in pH and acid-neutralizing capacity; annual nitrate fluxes were dominated by high-discharge periods. Interannually, the fluxes at each site varied by 1-2 orders of magnitude, but the patterns of N leakage displayed considerable synchrony with outbreaks of gypsy moth caterpillar defoliation that began in the late 1980s and early 1990s in this region. N leakage from forested watersheds apparently lagged the initial defoliation by several months to perhaps a year or more. Defoliation outbreaks by the gypsy moth caterpillar (or other herbivorous pests) thus provide an alternative explanation of N leakage from forest ecosystems. Poorly documented insect defoliations, rather than premature N saturation of intact forest ecosystems, need to be considered as a possible explanation of N leakage from forested watersheds in the mid-Appalachian region and elsewhere.
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: Lake and watershed management strategies and recent environmental legislation dictate that nonpoht nutrient sources associated with storm water runoff must be assessed. Accordingly, a nutrient flu assessment for phosphorus and nitrogen is conducted through an extensive literature review of nutrient export studies. These studies are reevaluated. The nutrient export coefficients are screened according to sampling design criteria and compiled according to land use. The ecological mechanisms within each land use influencing the magnitude of nutrient flux are also discussed
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Changes of land use in coastal watersheds to residential development with on-site sewage disposal represent a potential change in both the quantity and quality of nutrient inputs to coastal marine systems. Measurements of dissolved N and phosphate P in septic system effluent indicated initial concentrations 100-1000-fold greater than receiving coastal waters, with inorganic N/P ratios (17/1) similar to phytoplankton growth requirements. Transformations of organic and inorganic N and retention of inorganic P occurred in the initial meters of groundwater transport with substantial (almost-equal-to 70%) nitrification of effluent ammonium to nitrate and retention of phosphate by the soil (almost-equal-to 60%). The degree of initial transformation and retention was directly related to unsaturated infiltration distance and is consistent with the requirements of these processes for oxidizing conditions. At greater distances (10-100 m), over 99% of the total dissolved N occurred as nitrate, phosphate concentrations were reduced to background levels, and groundwater N/P ratios exceeded 2500/1. The greater the importance of high-N, low-P groundwater inputs to the nutrient balance of a coastal water body, the greater the potential for shifts in the nutrient which limits primary production.
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Data from 85 sites across the United States were used to estimate concentrations and yields of selected nutrients in streams draining relatively undeveloped basins. Flow-weighted concentrations during 1990–1995 were generally low with median basin concentrations of 0.020, 0.087, 0.26, 0.010, and 0.022 milligrams per liter (mg/L) for ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus, respectively. The flow-weighted concentration of nitrate exceeded 0.6 mg/L in only three basins. Total nitrogen exceeded 1 mg/L in only four basins, and total phosphorus exceeded 0.1 mg/L in only four basins. The median annual basin yield of ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus was 8.1, 26, 86, 2.8, and 8.5 kilograms per square kilometer, respectively. Concentrations and yields of nitrate tended to be highest in northeastern and mid-Atlantic coastal states and correlated well with areas of high atmospheric nitrogen deposition. Concentrations and yields of total nitrogen were highest in the southeastern part of the nation and in parts of the upper Midwest. In the northeast, nitrate was generally the predominant form of nitrogen, and in the southeast and parts of the upper Midwest, organic nitrogen was the dominant form. Concentrations of total phosphorus were generally highest in the Rocky Mountain and Central Plain states.
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The Choptank River basin is a coastal plain catchment dominated by agriculture (52% of land use). We summarize an 11 year data set of discharge and chemistry from a gauged subbasin. Discharge exhibited seasonal variations driven by seasonal evapotranspiration. There were double seasonal maxima of pH, NH4 +, NO3 -, total N, Fe, and total P concentrations in late spring and fall as the saturated zone rose and fell within the soil. Significant interannual variability in discharge was the result of rainfall variation. There were positive nterannual trends in NO3 - concentrations and negative interannual trends in NH4 + and PO4 3- concentrations. These data were combined to estimate N and P export coefficients of 3-11 kg N ha-1 yr-1 and 0.14-0.66 kg P ha-1 yr-1, driven primarily by interannual variations in discharge. These export coefficients are low compared to other coastal plain watersheds dominated by agriculture and may be responsible for the small anthropogenic effects in the Choptank estuary compared to other Chesapeake drainages.
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High concentrations of nitrate in groundwater and surface water make it unsuitable as drinking water. Furthermore, high nitrogen emissions to the marine environment cause eutrophication with increased algal growth, changes in the biological communities and deoxygenation. Both groundwater protection and eutrophication are significant environmental issues on the European agenda. The main source of nitrogen in Europe is agricultural leaching from fields caused by excess inputs of fertilisers and manure compared to harvested output. This is especially evident in North-western Europe. It is reflected in river concentrations of nitrate, which are significantly highest in Western Europe. Since the late 1970s, nitrate concentrations have increased all over Europe reflecting intensification of agriculture. High concentrations occur in groundwater in most parts of Europe and most coastal areas of Europe show signs of eutrophication. In Denmark the Parliament in 1987 decided on the Action Plan on the Aquatic Environment (I), which included measures in several sectors. For agriculture the target was a 49% reduction of nitrogen emissions in order to improve groundwater quality and reduce marine loading. In the early 1990s monitoring results and modelling documented that the measures taken in 1987 as well as additional measures taken were insufficient to reach the target. In late 1997 Action Plan on the Environment (II) was agreed maintaining the target, which shall be reached by a range of measures including restoration of wetlands, afforestation, groundwater protection areas, improved animal fodder utilisation, more stringent requirements on livestock density (harmony criteria), more stringent nitrogen utilisation requirements for animal manure, and reduced nitrogen standards for crops. At the European level, the Nitrates Directive has as objective to reduce nitrate emissions to groundwater and surface water. The fact that no country yet has implemented the Directive, clearly documents the difficulties in taking efficient environmental measures in agriculture. The recent Danish policy measures show that there is no easy and cheap solution, which is also politically acceptable. Therefore a wide range of measures are needed to reduce a significant European environmental problem.