Article

Nitrogen loads to estuaries: Using loading models to assess the effectiveness of management options to restore estuarine water quality

Authors:
  • Marine Biological Laboratory, Woods Hole Ma USA
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Abstract

Nitrogen (N) loading to estuaries has become a major concern for coastal planners. As urban development on coastal watershed continues, estuaries and bays are becoming more eutrophic, and cascading effects are being felt at every trophic level. Managers and stakeholders need to have a suite of effective management tools that can be applied to coastal watersheds to minimize the effects of eutrophication. We applied an N loading model and an estuarine loading model to examine the effectiveness of a suite of potential management options that could be implemented in Waquoit Bay, Cape Cod, Massachusetts. This estuarine system is a case study in which we can explore the relative potential effectiveness of decreasing inputs from wastewater and fertilizer-derived N, diverting nitrogenous runoff from impervious surfaces, altering zoning ordinances, preserving forested tracts of land as well as freshwater and saltwater wetlands, harvesting macroalgae, dredging estuary channels, and exterminating waterfowl. From a combination of simulation results, assessment of the magnitude of loads from different sources, and through different land covers, and the additional consideration of feasibility we identified management options with high, intermediate, and low potential effectiveness. Improvement of septic system performance, use of zoning regulations, preservation of forested tracts and freshwater bodies, and conservation of salt marshes emerged as the most promising avenues to manage N loads in our system. Installation of wastewater treatment plants, controlling fertilizer use, and harvesting macroalgae would potentially have intermediate success. Diversion of runoff from impervious surfaces, dredging, and extermination of waterfowl show little promise at reducing N loads. These conclusions potentially set priorities for decision-makers charged with the management of Waquoit Bay. The same procedures applied to another watershed-estuary system with different land covers and different estuarine features may differ. Evaluation studies like this need to be done for any particular site, since the watershed-estuary coupling and the loads delivered to the receiving estuary could differ. The Waquoit Bay case study provides an example of a protocol that leads to identification of the most promising management options.

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... In particular, land-derived nitrogen (N) loading in estuaries has increased recently as land use has intensified in watersheds (JORDAN and WELLER, 1996;JAWORSKI et al., 1997;BOWEN and VALIELA, 2004). An increase in the supply of N to estuaries stimulates eutrophication and causes phytoplankton and macroalgae blooms (LAVERY et al., 1991;DUAR-TE, 1995;VALIELA et al., 1997;HAUXWELL et al., 2001), which has an ecological impact. ...
... An increase in the supply of N to estuaries stimulates eutrophication and causes phytoplankton and macroalgae blooms (LAVERY et al., 1991;DUAR-TE, 1995;VALIELA et al., 1997;HAUXWELL et al., 2001), which has an ecological impact. The increased N loads occurring throughout the world (VITOUSEK et al., 1997) are largely driven by changes in land use in watersheds, such as increased urban and agricultural development (CONSTANZO et al., 2003 andBOWEN andVALIELA, 2004). Global production of fertilizers has also increased markedly in recent decades (SMIL, 1997;GALLOWAY, 1998) and fertilizers are major sources of nutrients to some estuaries (LEE and OLSEN, 1985;BOYNTON et al., 1995;JORDAN et al., 1997;SIERRA et al., 2002). ...
... An increase in the supply of N to estuaries stimulates eutrophication and causes phytoplankton and macroalgae blooms (LAVERY et al., 1991;DUAR-TE, 1995;VALIELA et al., 1997;HAUXWELL et al., 2001), which has an ecological impact. The increased N loads occurring throughout the world (VITOUSEK et al., 1997) are largely driven by changes in land use in watersheds, such as increased urban and agricultural development (CONSTANZO et al., 2003 andBOWEN andVALIELA, 2004). Global production of fertilizers has also increased markedly in recent decades (SMIL, 1997;GALLOWAY, 1998) and fertilizers are major sources of nutrients to some estuaries (LEE and OLSEN, 1985;BOYNTON et al., 1995;JORDAN et al., 1997;SIERRA et al., 2002). ...
Article
Water quality plays a very important role in the ecological balance and economic development of coastal and estuarine areas. However, these areas have been progressively degraded in recent decades due to different factors, including an increase in nutrient and pollutant loads introduced into the system, which may cause eutrophication problems. This paper analyzes the water quality of one such area, Cullera Bay, located on the Spanish Mediterranean coast. This study focuses on the main sources and sinks of pollutant substances and the relationship between the distribution of these substances within the bay and local meteorological and oceanographic conditions. Two main sources of nutrients and pollutants were identified: the discharges of the Júcar River and the marine outfall, although other secondary sources are also present. The river discharge varies greatly depending on the season. The freshwater it carries is very rich in nutrients due to the presence of fertilizers and pesticides from its agricultural use. The domestic wastewater discharged through the marine outfall is occasionally untreated, particularly in the summer, when the tourist population increases and the capacity of the water treatment plant is exceeded. This study is based on data recorded during nine field campaigns carried out in the area in 2002 and 2003 and numerical simulations of hydrodynamics and pollutant dispersion. By analyzing the field data and the numerical simulation results, wind is identified as the main driving factor in the bay because the other possible driving factors either have negligible effects (tide), affect only a very localized area (waves, usual river discharges) or are infrequent (storm surges, river floods).
... Anthropogenic manipulation of surface and subsurface freshwater affects the physical and biogeochemical balance of estuarine ecosystems by altering the input, transport, and assimilation of water, inorganic nutrients, particulate organic mat-ter (POM), dissolved organic matter, toxic metals, and organopollutants (Sanger et al. 1999a,b;Dame et al. 2000;Lerberg et al. 2000;Bowen and Valiela 2004). The specific responses of a particular tidal ecosystem to changes in external factors vary with the composition of the inputs and gradients in geomorphology, physical transport, and internal biogeochemical cycling (Hopkinson and Vallino 1995;Cloern 2001;Aikman and Lanerolle 2005). ...
... Effects of nutrient overenrichment historically observed in other regions appear to have been mitigated by high tidal flushing in the salt marsh dominated ecosystems of the southeastern U.S. (Bricker et al. 1999;Dame et al. 2000). Growing amounts of impervious cover in coastal watersheds in the southeast has heightened the sensitivity of tidal creek ecosystems to both chronic and episodic inputs of materials (Beach 2002;Verity 2002;Bowen and Valiela 2004;Holland et al. 2004). ...
... It is a critical time in the management of southeastern U.S. estuaries (Mallin et al. 2001;Holland et al. 2004). In other regions such as the northeastern U.S., environmental management has emphasized habitat clean up and reclamation (Bowen and Valiela 2004). Proactive opportunities exist in the southeast because there is still time to mitigate the spread of impervious cover, many multiannual, interdisciplinary studies and monitoring programs that have started over the past decade have matured, and dynamic interactions among basin morphometry, tidal exchange, and biogeochemical cycling help modulate material inputs to salt marsh estuaries (Bricker et al. 1999;Dame et al. 2000;Wenner and Geist 2001;Verity 2002;Holland et al. 2004). ...
Article
Full-text available
Many coastal ecosystems are undergoing anthropogenic stress from large increases in population and urbanization. In many regions changes in freshwater and material inputs to the coastal zone are altering the biogeochemical and biological capacities of ecosystems. Despite increased watershed inputs, large tidal volumes and flushing indicative of macrotidal estuaries can modulate the fate of introduced materials masking some of the symptoms of eutrophication. The Land Use Coastal Ecosystem Study (LU-CES) examined linkages between land use and environmental properties of Malind and Okatee Creeks in South Carolina from 2001 to 2004. The objectives of this particular study were to assess the hydrography of the two macrotidal creek ecosystems, explore differences in dissolved oxygen (DO), and develop a better understanding of the variations in primary and benthic secondary production in southeastern creek ecosystems. Depth, pH, salinity, and DO were reduced and more variable in Malind Creek than in Okatee Creek, although both creeks had strong semidiurnal frequencies in salinity time signatures. While time series analyses of DO saturation in Malind Creek revealed a dominant semidiurnal pattern, Okatee Creek had a distinctly diel DO pattern. The strongly semidiurnal fluctuations in DO and reduced flushing time indicated that biological processes were not fast enough to influence DO in Malind Creek. The Okatee Creek system had a much greater storage volume, a wider marsh, and a dominant 25-h DO frequency. These attributes contributed to an estimated 8–10 times more phytoplankton-based carbon in Okatee Creek and twice the annual benthic production. As expected from their proximity to the upland, low surface area, and high organic content, both ecosystems were net heterotrophic. This fundamental understanding of tidal creek hydrography is being used to help define linkages among differential watershed land uses, flushing characteristics, and levels of biological production in coastal ecosystems of the southeastern United States.
... Excessive amounts of nitrogen are linked to eutrophication, hypoxia, food web alteration, and harmful algal blooms in coastal waters (Howarth et al., 2000). Anthropogenic sources of nitrogen, particularly wastewater disposal, are a significant cause of these degrading effects (USEPA, 1993;Bowen and Valiela, 2004;Williamson et al., 2017). Excessive nitrogen, among other chemical pollutants, contributes to water quality characteristics that exceed state mandates for designated industrial, agricultural, wildlife, and recreational uses. ...
... However, limited information is currently available on quantitative nonmarket (e.g., Bellver-Domingo and Hernández-Sancho, 2018) or qualitative non-monetary (Martin et al., 2018) valuation methods across Cape Cod. Likewise, less information is available to trace environmental outcomes to OWTS performance (Bowen and Valiela, 2004). ...
Article
This article aims to understand decision making under uncertainty and risk, with a case study on Cape Cod, Massachusetts. Decision makers need to consider imperfect information on the cost and effectiveness of advanced nitrogen-removing on-site wastewater treatment systems as options to mitigate water quality degradation. Research included modeling nitrogen load reduction to impaired coastal waters from seven treatment system technologies and eliciting expert knowledge on their costs. Predictions of nitrogen load removal and cost for each technology incorporated variation in effectiveness and uncertainty in household water use, costs, and expert confidence in costs. The predictions were evaluated using the Pareto efficiency concept to reveal tradeoffs between cost and effectiveness. The stochastic dominance index was used to identify preferred technologies for risk- averse decision making, assuming no further learning is possible. Lastly, the predictions were combined into a cost-effectiveness metric to estimate the expected payoff of implementing the best treatment system in the face of uncertainty and the expected payoff of learning which treatment systems are most cost-effective over time. The expected value of perfect information was calculated as the difference between the expected payoffs. Three technologies revealed Pareto efficient tradeoffs between cost and effectiveness, whereas one technology was the preferred risk-averse option in the absence of future learning. There was a high expected value of perfect information, which could motivate adaptive management on Cape Cod. This research demonstrated decision analysis methods to guide future research and decision making toward meeting water quality objectives and reducing uncertainty.
... Increased inputs of nitrogen sources to estuarine systems can influence primary producer uptake, which may increase phytoplankton productivity and affect carbon sources at the base of the food web (McClelland and Valiela 1998b;Twomey et al. 2005). Little is known of how blue crab food sources vary along salinity and estuarine systems (Duarte 1995;Micheli 1999;Bowen and Valiela 2004). ...
... Nitrogen inputs to river estuaries can affect food sources available to higher trophic level consumers (Bowen and Valiela 2004). Although original sources of nitrate (e.g., municipal waste versus fertilizer) were not identified, observed differences in nitrate concentrations may have influenced blue crab food sources. ...
Article
Full-text available
The present study focused on detecting variations in trophic relationships among blue crab (Callinectes sapidus) consumers according to water quality along two estuaries in North Carolina. Stable isotope (δ15N and δ13C) analyses of particulate organic matter and bivalve (Rangia cuneata andCorbicula fluminea) food sources were examined in combination with an Isosource mixing model. Results suggest that blue crab δ13C values increased significantly with increasing salinity from upper to lower sites along the Neuse River estuary (NRE; R2 = 0.87, p 2 = 0.92, p 15N values and nitrate concentrations for the NRE (R2 = 0.48, p = 0.12). This study found that blue crab δ13C values increased with salinity from upper to lower regions along both estuaries. Results suggest that blue crab production may have used alternative food sources that were isotopically (δ13C) depleted, especially in the upper NRE, and enriched sources in the mid to lower regions of both estuaries. Consumers sampled from the upper NRE may be influenced by higher nitrogen input from urban land use and municipal wastewater.
... Toxic cyanobacteria directly affect drinking water safety in cities and towns, and seriously affect the structure and function of aquatic ecosystems once bloom occurred [4]. In general, estuaries have relatively high number of nonpoint and point sources of pollution, and are the last barrier preventing exogenous pollution of reservoirs [5,6]. ...
... Total nitrogen varied seasonally, with the peak during January and February; TN was much lower at EXP than at REF ( Figure 2D). COD varied at REF from 6.65 to 36.66 mg/L, and at EXP from 4.63 to 23.95 mg/L ( Figure 2E). ...
Article
Full-text available
An integrated physical and ecological engineering experiment for ecological remediation was performed at the Maixi River bay in Baihua Reservoir Guizhou Province, China. The results show that eutrophic parameters, such as total nitrogen, total phosphorus, chlorophyll a and chemical oxygen demand from the experimental site (enclosed water) were significantly lower than those of the reference site. The largest differences between the sites were 0.61 mg x L(-1), 0.041 mg x L(-1), 23.06 microg x L(-1), 8.4 mg x L(-1) respectively; experimental site transparency was > 1.50 m which was significantly higher than that of the reference site. The eutrophic index of the experimental site was oligo-trophic and mid-trophic, while the control site was mid-trophic state and eutrophic state. Phytoplankton abundance was 2 125.5 x 10(4) cells x L(-1) in June, 2011 at the control site,but phytoplankton abundance was lower at the experimental site with 33 x 10(4) cells x L(-1). Cyanobacteria dominated phytoplankton biomass at both sites, however the experimental site consisted of a higher proportion of diatoms and dinoflagellates. After more than one year of operation, the ecological engineering technology effectively controlled the occurrence of algae blooms, changed phytoplankton community structure, and controlled the negative impacts of eutrophication. Integrating physical and ecological engineering technology could improve water quality for reservoirs on the Guizhou plateau.
... Toxic cyanobacteria directly affect drinking water safety in cities and towns, and seriously affect the structure and function of aquatic ecosystems once bloom occurred [4]. In general, estuaries have relatively high number of nonpoint and point sources of pollution, and are the last barrier preventing exogenous pollution of reservoirs [5,6]. ...
... Total nitrogen varied seasonally, with the peak during January and February; TN was much lower at EXP than at REF ( Figure 2D). COD varied at REF from 6.65 to 36.66 mg/L, and at EXP from 4.63 to 23.95 mg/L ( Figure 2E). ...
Article
From June 2009 to August 2011, an integrated physical and ecological engineering experiment (PEE) for ecological remediation was conducted in the Maixi river estuary in Baihua Reservoir. An experiment site (EXP) inside, and a reference site (REF) outside, the engineering enclosure were selected. Total nitrogen (TN), total phosphorus (TP), Chlorophyll-a (Chl-a), and chemical oxygen demand (COD) at EXP were significantly lower than at REF; and the greatest differences were 1.00 mg/L, 0.04 mg/L, 23.06 μg/L, and 8.40 mg/L, respectively. Transparency at EXP was dramatically higher than at REF. The trophic index state (TSI) was between oligotrophic and mesotrophic at EXP, between mesotrophic and eutrophic at REF. Phytoplankton abundance in June 2011 was 2100×104 cells/L at REF, but lower at EXP with 33×104 cells/L. Cyanobacteria dominated phytoplankton biomass at both sites, but a higher proportion of diatoms and dinoflagellates was found at EXP. Rotifers were the main estuarine zooplankton. Copepod abundance was significantly different among the sites (p<0.01), with greater abundance at EXP. In general, eutrophication was controlled by the PEE, which could be adjusted to improve water quality.
... As pointed out by Grober-Dunsmore et al. (2009), connectivity is an important concept inherited from landscape ecology and now applied to define a marine seascape. and organic materials (Bowen and Valiela, 2004;Mitsch and Gosselink, 2000;Nelson and Zavaleta, 2012;Shapiro et al., 2010). Coral reefs in turn shelter these coastal habitats by buffering oceanic waves and currents and slowing down periodic storm surge (Berkström et al., 2012;Harborne et al., 2006;Moberg and Rönnbäck, 2003). ...
... Water and pollution control by mangroves, seagrass beds, marsh, and other coastal habitats not only benefit nearby human populations, activities, and property but also protect near-shore marine habitats, thus enhancing their goods and services (Berkström et al., 2012;Harborne et al., 2006;Bowen and Valiela, 2004;Mitsch and Gosselink, 2000;Moberg and Rönnbäck, 2003;Nelson and Zavaleta, 2012;Shapiro et al., 2010). Increasingly, economists are estimating the benefits associated with this service, in terms of improved human health, residential property value, and support for marine fisheries (Breaux et al., 1995;Leggett and Bockstael, 2000;Massey et al., 2006;Smith, 2007;Smith and Crowder, 2011;Turner et al., 2004;van der Meulen et al., 2004). ...
Article
In ecology, the term seascape is used to describe a complex dynamic patchwork of interconnected marine and near-shore habitats (e.g., coral reef, sea grass, open water, mangrove, sandy beaches). This monograph examines this novel way of viewing the marine environment and discusses how economics can contribute to this approach to provide new analytical, management, and policy insights. A simple model of a twohabitat marine system (coral reefs and mangroves) is developed. The model is used to illustrate that, even if the focus is on whether or not to develop only the coastal habitat (i.e., mangroves), taking into account its connectivity with the rest of the seascape (i.e., coral reef) can affect the decision as to how much and which part of the coastal should be developed. The impact of seascape connectivity is examined for three marine ecosystem services: storm protection, habitat–fishery linkages, and water pollution and sediment control.
... As pointed out by Grober-Dunsmore et al. (2009), connectivity is an important concept inherited from landscape ecology and now applied to define a marine seascape. and organic materials (Bowen and Valiela, 2004;Mitsch and Gosselink, 2000;Nelson and Zavaleta, 2012;Shapiro et al., 2010). Coral reefs in turn shelter these coastal habitats by buffering oceanic waves and currents and slowing down periodic storm surge (Berkström et al., 2012;Harborne et al., 2006;Moberg and Rönnbäck, 2003). ...
... Water and pollution control by mangroves, seagrass beds, marsh, and other coastal habitats not only benefit nearby human populations, activities, and property but also protect near-shore marine habitats, thus enhancing their goods and services (Berkström et al., 2012;Harborne et al., 2006;Bowen and Valiela, 2004;Mitsch and Gosselink, 2000;Moberg and Rönnbäck, 2003;Nelson and Zavaleta, 2012;Shapiro et al., 2010). Increasingly, economists are estimating the benefits associated with this service, in terms of improved human health, residential property value, and support for marine fisheries (Breaux et al., 1995;Leggett and Bockstael, 2000;Massey et al., 2006;Smith, 2007;Smith and Crowder, 2011;Turner et al., 2004;van der Meulen et al., 2004). ...
Article
In ecology, the term seascape is used to describe a complex dynamic patchwork of interconnected marine and near-shore habitats (e.g., coral reef, sea grass, open water, mangrove, sandy beaches). This monograph examines this novel way of viewing the marine environment and discusses how economics can contribute to this approach to provide new analytical, management, and policy insights. A simple model of a twohabitat marine system (coral reefs and mangroves) is developed. The model is used to illustrate that, even if the focus is on whether or not to develop only the coastal habitat (i.e., mangroves), taking into account its connectivity with the rest of the seascape (i.e., coral reef) can affect the decision as to how much and which part of the coastal should be developed. The impact of seascape connectivity is examined for three marine ecosystem services: storm protection, habitat-fishery linkages, and water pollution and sediment control.
... ,Valiela and Bowen 2002, Bowen and Valiela 2004, Carmichael et al. 2004, Latimer and Charpentier 2010, Williamson et al. 2017, the NLM has been successfully applied in Barnegat Bay, New Jersey(Bowen et al. 2007), Great South Bay, New York(Kinney and Valiela 2011), Port Mouton Bay, Nova Scotia (McIver et al. 2018), and coastal lagoons in the Delmarva Peninsula ...
Article
Full-text available
Nitrogen (N) pollution is arguably the single greatest threat to coastal water quality in the United States. In the state of Massachusetts, sustainable management of cranberry agriculture requires detailed understanding of potential sources and losses of N, which can contribute to impaired coastal waters. Given the complexity of N transport processes, models are often used to quantify the amount of N delivered from cranberry farms to coastal waters. However, ambiguities in model parameters, inconsistencies in deriving N loading rates, and inaccuracies in spatial coverages leave open questions about the contribution of cranberry agriculture to impaired coastal waters. In this study, we synthesize the methods, assumptions, and results of all N budget studies conducted in cranberry farms from 1995 to 2019. We propose a new analytical framework for measuring N fertilizer export from cranberry farms which includes our best understanding of N retention and transport in cranberry farms. We then apply our results to two watershed land‐use models (Massachusetts Estuaries Project Linked Watershed‐Embayment Model, LM; the Waquoit Bay Nitrogen Loading Model, NLM) to quantify N loads contributed by cranberry farms to the highly eutrophic Wareham River estuary. We find that the LM and NLM are in close agreement with respect to the amount of N delivered from cranberry farms to the Wareham River estuary. In our application of the LM, we estimated that 7791 kg N·yr−1 from cranberry farms, or 15% of the total N load, reached the estuary. By comparison, we found that the NLM estimated slightly higher N loads contributed by cranberry farms to the estuary: 8365 kg N·yr−1, or 16% of the total N load. However, the models gave contrasting estimates of unattenuated N loads from cranberry farms (9670 kg N·yr−1, LM; 12,870 kg N·yr−1, NLM) and the amount of N transmitted through the watershed to the estuary (81% LM; 65% NLM).
... It appears that estuaries in CT were more susceptible to additional watershed development than estuaries in MA and RI; although all estuaries in the region are affected by wastewater from watershed development. This information has management implications for source reduction ( Bowen and Valiela, 2004) as well as best management practices in the watersheds for the attenuation of nitrogen. Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Row A Row B Row C Row D Row E Fig. 4. Graphs showing frequency distributions of the total nitrogen loading rates (Col. ...
Article
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Excess nitrogen inputs to estuaries have been linked to deteriorating water quality and habitat conditions which in turn have direct and indirect impacts on aquatic organisms. This paper describes the application of a previously verified watershed loading model to estimate total nitrogen loading rates and relative source contributions to 74 small-medium sized embayment-type estuaries in southern New England. The study estuaries exhibited a gradient in nitrogen inputs of a factor of over 7000. On an areal basis, the range represented a gradient of approximately a factor of 140. Therefore, all other factors being equal, the study design is sufficient to evaluate ecological effects conceptually tied to excess nitrogen along a nitrogen gradient. In addition to providing total loading inputs rates to the study estuaries, the model provides an estimate of the relative contribution of the nitrogen sources from each watershed to each associated estuary. Cumulative results of this analysis reveal the following source ranking (means): direct atmospheric deposition (37%), ≈wastewater (36%), >indirect atmospheric deposition (16%) > fertilizer (12%). However, for any particular estuary the relative magnitudes of these source types vary dramatically. Together with scientific evidence on symptoms of eutrophication, the results of this paper can be used to develop empirical pressure-state models to determine critical nitrogen loading limits for the protection of estuarine water quality.
... The dominant primary producers (phytoplankton, sediment microalgae, macroalgae, Spartina alterniflora) of marshestuaries on the U.S. Atlantic coast are largely nitrogen limited (Morris and Bradley, 1999;Holmes et al., 2000;Twomey et al., 2005). RAIN, SURF, and GW pathways introduce new N to coastal ecosystems (Paerl et al., 2001;Bowen and Valiela, 2004). As the recipient of external nutrient inputs, a limiting factor in phytoplankton growth, and the intermediary in model bio-geochemical cycling, DN processes were central to ecosystem model functioning. ...
Article
Tidal creek ecosystems integrate the coastal landscape by linking upland environments to the coastal ocean. These ecosystems feature a combination of sinuous creek beds with wide lateral wetlands interspersed with mud flats and oyster reefs. Previous studies demonstrated negative relationships between habitat quality and indicators of watershed urbanization. However, predicting trends in ecological robustness for a number of irregularly branched tidal ecosystems with different watershed attributes, material inputs, and flushing is a difficult task. This study began to address this task by using a simulation framework to assess water column and sediment ecological processes in two distinct tidal creek ecosystems in South Carolina (Malind Creek versus Okatee Creek). Biogeochemical cycling in these creeks fluctuates with hourly, daily, and seasonal changes in tidal exchange, freshwater and material inputs, and autochthonous primary production. Over 2 years simulation based on 2001–2002 input data an estimated 4–5 times more freshwater entered Okatee Creek than Malind Creek even though Okatee Creek watershed and basin areas are only 2.5X larger. Phytoplankton consumed approximately 70% of all water column dissolved nitrogen annually with autochthonous production the primary source of particulate and dissolved organic carbon (OC) to the sediments. Okatee Creek had approximately 7X the net deposition of OC to the sediments were it combined with sediment microalgal biomass to drive benthic secondary production. Differences in physical transport in salt marsh dominated tidal creeks influence the capacity to process, transform, and sequester introduced materials. Modifications to the simulation model will include improved depth, volume, and tidal exchange for more realistic prediction of effective concentrations. This modeling framework connects watershed and atmospheric material loading to estuarine productivity, has been used to assess differences in ecosystem metabolism with changes in environmental drivers, and provides the foundation for a suite of sub-models to forecast the potential effects of relative sea level rise for a variety of nearshore environments.
... Modelling techniques exist for estimating watershed-wide pollutant transport (e.g. nitrogen load) to receiving waters (Borah and Bera, 2004;Bowen and Valiela, 2004). While watershed models such as Hydrologic Simulation Program Fortran (HSPF) can be used to estimate loads for these unmonitored areas, often data requirements (e.g. ...
Article
Full-text available
Pollutant load reductions are often required to restore aquatic ecosystems experiencing eutrophication. Loads can be estimated using watershed models or data from monitoring stations, however data availability can limit the timeliness or comprehensiveness of the load estimates. We developed an approach to address this challenge that used watershed model results to estimate the proportion of annual nonpoint source nitrogen (N), phosphorus (P) and sediment (Sed) loads derived from unmonitored catchments. This proportion was multiplied by the nonpoint portion of United States Geological Survey (USGS) estimated annual river loads to account for annual variation in hydrologic conditions. Total loads were calculated as the sum of measured river loads, reported point sources from unmonitored areas and the estimated nonpoint source loads from unmonitored catchments. We applied this approach to the Chesapeake Bay because of its socio-economic and ecological importance. Median watershed loads for N, P and Sed were 140, 6.4 and 3030 Mg year−1, respectively (1990–2004). Nonpoint source loads from the monitored areas constituted the greatest source of N, P and Sed (55, 47 and 74% respectively) to the Bay. The high N, P and Sed yield rates (7.3, 0.38 and 99 kg ha−1 year−1, respectively) from nonpoint loads originating from unmonitored areas near the Bay resulted in 25, 32 and 26% (N, P and Sed, respectively) of the Bay's total loads (excluding direct atmospheric deposition, shoreline erosion and oceanic inputs). Disproportionately high loads of P and Seds were associated with years that experienced elevated discharge whereas N loads were directly related to discharge. Error estimates indicated that our methods were most reliable for N (±6%) but reasonable for P (±22%) and provide an effective technique for the timely estimation of pollutant loads from watersheds with unmonitored catchments. Management strategies that decrease N deposition and reduce runoff to control P and Sed transport will effectively reduce pollutant loads. Published in 2010 by John Wiley & Sons, Ltd.
... Many complex processes interact to structure the phytoplankton community. Deteriorating water quality and ecological functioning within estuaries have become major concerns due to eutrophication caused by human activity (Billen et al., 2001;Kirby-Smith et al., 2003;Bowen and Valiela, 2004). Nutrients are introduced into the water column not only from estuarine processes, but also processes occurring within the entire upstream watershed. ...
Article
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Phytoplankton and environmental variables were measured monthly from July 2009 to August 2011 in the Maixi River from the estuary to Baihua Reservoir in the Maotiao River catchment, southwestern China, to understand phytoplankton community structure and environmental factors. The relationship between phytoplankton community structure and environmental factors including hydrological, meteorological, physical, and chemical variables were explored using multivariate analysis. A total of 81 taxa of phytoplankton were identified, which were mainly composed of chlorophyta, bacillariophyta, and cyanobacteria. The phytoplankton community was dominated by Pseudanabaena limnetica during summer and fall and by Cyclotella meneghiniana during winter and spring. The abundance of phytoplankton ranged from 0.24×104 cells/L to 33.45×106 cells/L, with the minimum occurring during February 2010 and the maximum during July 2009. The phytoplankton community was dominated mainly by cyanobacteria from April to September, and by bacillariophyta and pyrrophyta from October to March. Canonical correspondence analysis showed that temperature, pH values, and orthophosphate were the most important driving factors regulating the composition and dynamics of the phytoplankton community in the estuary. Cyanobacteria and euglenophyta abundance and biomass were affected mainly by temperature and pH values, while most chlorophyta and bacillariophyta were influenced by the concentrations of nutrients.
... River-derived nutrient inputs into estuaries have tripled between the 1970s and the 1990s (Smith et al. 2003) and are predicted to continue increasing in the next decades as a result of population growth on coastal watersheds (Seitzinger et al. 2002). The relationships between land use and riverine exports (Bowen and Valiela 2004;Brush 2009;McKee et al. 2000) as well as the biogeochemical processes regulating nutrient cycling within estuaries (Boynton et al. 1995;Seitzinger et al. 2005) have been relatively well studied. Better understanding of the contribution of groundwater discharge to nutrient cycling represents a major gap in our knowledge about estuaries (Statham 2012). ...
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Four months of daily nutrient and radon (a natural groundwater tracer) observations at the outlet of a heavily drained coastal wetland illustrated how episodic floods and diffuse groundwater seepage influence the biogeochemistry of a sub-tropical estuary (Richmond River, New South Wales, Australia). Our observations downstream of the Tuckean Swamp (an acid sulphate soil floodplain) covered a dry stage, a flood triggered by a 213-mm rain event and a post-flood stage when surface water chemistry was dominated by groundwater discharge. Significant correlations were found between radon and ammonium and N/P ratios and between radon and dissolved organic nitrogen (DON) during the post-flood stage. While the flood lasted for 14 % of the time of the surface water time series, it accounted for 18 % of NH4, 32 % of NOx , 66 % of DON, 58 % of PO4 and 55 % of dissolved organic phosphorus (DOP) catchment exports. Over the 4-month study period, groundwater fluxes of 35.0, 3.6, 36.3, 0.5 and 0.7 mmol m−2 day−1 for NH4, NOx , DON, PO4 and DOP, respectively, were estimated. The groundwater contribution to the total surface water catchment exports was nearly 100 % for ammonium, and <20 % for the other nutrients. Post-flood groundwater seepage shifted the system from a DON to a dissolved inorganic N-dominated system and doubled N/P ratios in surface waters. We hypothesise that the Richmond River Estuary N/P ratios may reflect a widespread trend of tidal rivers and estuaries becoming more groundwater-dominated and phosphorus-limited as coastal wetlands are drained for agriculture, grazing and development.
... Many complex processes interact to structure the phytoplankton community. Deteriorating water quality and ecological functioning within estuaries have become major concerns due to eutrophication caused by human activity (Billen et al., 2001;Kirby-Smith et al., 2003;Bowen and Valiela, 2004). Nutrients are introduced into the water column not only from estuarine processes, but also processes occurring within the entire upstream watershed. ...
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The relationships between chlorophyll-a, phytoplankton abundance and 20 chemical, physical and biological water quality variables were studied by using principal component scores (PCs) in stepwise linear regression analysis (SLR) to simulate chlorophyll-a and phytoplankton abundance at a karst deep reservoir, southwest of China. Score values obtained by PC scores were used as independent variables in multiple linear regression models. The following models were used to simulate chlorophyll-a and abundance of Cyanobacteria, Chlorophyta, Bacillariophyta, and Pyrrophyta respectively: chlorophyll-a1 = 10.501 + 1.390 (score 1) (P < 0.01), chlorophyll-a 2 = 10.501 + 1.102 (score 1)−0.877 (score 2) (P < 0.05), log10 (Cyanobacteria) = 1.277−0.726 (score 2) (P < 0.05), log10 (Chlorophyta) = 3.927−0.150 (score 2) (P < 0.01), log10 (Bacillariophyta) = 4.872−0.131 (score 4) (P < 0.01) and log10 (Pyrrophyta) = 2.463 + 0.578 (score 1) (P < 0.05). The models could be used to simulate chlorophyll-a and phytoplankton abundance levels successfully, and revealed that DO, WD, Tem, TD, pH, NH4–N and TSS were the most important factors regulating the composition of chlorophyll-a and Pyrrophyta abundance. ORP, Cl−, SO42-, TN were the main factors affecting Chlorophyta and Cyanobacteria abundance. F− and Ca2+ were the main factors influencing the Bacillariophyta abundance.
... The red seaweed Porphyra yezoensis, grown on a large seaweed farm (300 ha) in China, removed approximately 50 kg per ha of nitrogen annually (He et al., 2008). Bowen and Valiela (2004) examined a potential bio-extraction of N via harvesting naturally abundant macroalgae. If the mean annual biomass of the standing stock of seaweed was harvested from Waquoit Bay, an estimated 15-66 kg N would be removed per hectare each year. ...
... In 2002 Beusekom et al. 2001;van Beusekom & de Jonge 2002). D e huidige nutriëntenconcentraties in de Waddenzee liggen dicht bij de bovengrens van de zeegrastolerantie (Bowen & Valiela 2004;Hauxwell et al. 2001Hauxwell et al. , 2003De Wit et al. 2005 Zaadstengeldeposities werden ondersteund door twee verschillende zaadbehoudtechnieken: zaadstengels met een laagje sediment bedekken of met netten overspannen. Het verschil in succes tussen de verschillende zaadbehoudtechnieken was zeer gering. ...
... If I correct for the double counting of poultry waste in the Boynton et al. (1993) (Valiela et al. 1992, Heberlig et al. 1997, Bowen and Valiela 2004. ...
... Concerns over the use of water resources are increasing as communities located on the lower reaches of rivers, and the estuaries they flow into, experience decreased water inputs and elevated nutrient levels due to anthropogenic activities in upstream drainage areas (Powell et al. 2002;Bowen and Valiela 2004;Savage 2005;Mathis et al. 2007;Arismendez et al. 2009). Nitrogen increases are of particular interest because they often drive eutrophication of estuarine systems, resulting in increased algal biomass, decreased submerged vascular plants, and changes or declines in resident fish populations (Hauxwell et al. 2001;Thronson and Quigg 2008). ...
Article
Freshwater inflows to Texas estuaries vary widely due to regional climate fluctuations and are being substantially altered by human activities. The natural abundance stable isotope ratios of carbon and nitrogen in oyster adductor muscle were used to acquire a time-integrated view of freshwater and nitrogen contributions to the Mission-Aransas National Estuarine Research Reserve in South Texas. The study objective was to determine the influence of inputs from the San Antonio and Guadalupe rivers, which deliver approximately 1.6 km³ of water to the mid-Texas coastal region annually. A transect of sampling stations extending from the head of San Antonio Bay (northeast of the Reserve boundary) to the Aransas Pass ship channel (roughly 70 km to the southwest) was visited multiple times between 2009 and 2011. Carbon isotopic values increased from approximately −25 to −17‰ while δ¹⁵N values decreased from approximately +16 to +10‰ between the bay and ship channel. This range of carbon isotope values translates into time-integrated freshwater fractions as high as 0.8 (1 = 100% fresh) at the most inland sampling station to freshwater fractions around zero approaching the Gulf of Mexico. Contributions from the San Antonio and Guadalupe rivers to waters of the reserve vary between wet and dry years, but overall, the data suggest that these rivers are persistent and substantial sources of fresh water and nitrogen to the reserve. This study emphasizes the importance of connectivity and lateral exchanges among bays/lagoons when considering potential sources of fresh water and nitrogen that control ecosystem structure and function.
... This separation of the river from the delta has altered water and nutrient budgets and is a primary cause of the massive wetland loss taking place in the delta (Boesch et al. 1994, Day et al. 2000a). Determination of the principal sources and sinks of freshwater and nutrients are important to understanding functioning, restoration, and management of coastal wetlands (Day et al. 2000a(Day et al. , 2000bGlasgow and Burkholder 2000;Oenema et al. 2003;Bowen and Valiela 2004). ...
... In fact, bird feces represents a perfect growth medium for large numbers of bacteria, viruses, fungi, and parasites (Sehgal, 2010). Birds feed on a variety of food items and in some species defecation can occur every 20 min (Bowen and Valiela, 2004). Digestion in birds involves many organs, each performing a specific function. ...
... Enhanced nutrient and sediment concentration pose serious problems for the maintenance and sustenance of biotic community of coastal ecosystem. On the other side, anthropogenic manipulation of surface and subsurface freshwater affects on physical and biogeochemical balance of estuarine ecosystems by altering the input, transport, and assimilation of water, inorganic nutrients, particulate organic matter (POM), dissolved organic matter, toxic metals, and organo-pollutants (Sanger et al., 1999;Bowen and Valiela, 2004). Therefore, present study was aimed to enlighten the hydro-chemical characteristics of Narmada estuary at different sites in relation to the Freshwater fraction ingress into tropical estuary, India during monsoon and summer seasons. ...
... Pollution by N and P from runoff has impacted fisheries and threatened fishery sustainability throughout history. Classical studies on places such as Waquoit Bay, Cape Cod, Massachusetts, have demonstrated that nutrient loading from development has dramatic impacts on estuaries, and even out into the open oceans, through wastewater and fertilizer impacts on N and P cycling (e.g., Bowen and Valiela 2004). Chesapeake Bay fisheries and seafood production remains detrimentally affected by development and by animal husbandry up the Potomac River. ...
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Globally, overall demand for agricultural products is expected to grow at 1.1% per year from 2005/2007-2050, down from 2.2% per year in the past four decades (Alexandratos and Bruinsma, 2012). Population growth, increases in per-capita consumption, and changes in diets leading to the consumption of more livestock products are the main drivers of expected changes.
... OWS are typically installed in aerobic soil environments that are favorable for nitrification (conversion of NH 4 to NO 3 ) to occur. Nitrate is mobile in groundwater and may discharge to surface waters contributing to increased nutrient loads and exacerbating eutrophic conditions (Bowen and Valiela, 2004). Denitrification (conversion of NO 3 to N 2 ) is a process for NO 3 removal from groundwater and generally requires anaerobic conditions, NO 3 , a carbon source and denitrifying microorganisms (Desimone and Howes, 1996). ...
Article
A permeable reactive barrier was installed between a large Onsite Wastewater System (OWS) and a monitoring well located downgradient from the OWS. Groundwater samples from the well had shown elevated and increasing concentrations of NO3--N (>20 mg L−1 for 2 years). The barrier was constructed using woodchips from various tree species that were placed in a trench excavated to approximately the same depth as the well which was experiencing elevated NO3 --N concentrations. Groundwater samples (5) were collected from the well between two weeks and four months after the barrier was installed. Groundwater NO3 --N concentrations dropped by an average of 5 mg L−1, while Dissolved Organic Carbon (DOC) concentrations increased by 11 mg L−1 and Cl concentrations stayed relatively stable (<2 mg L−1 increase). The data suggest that denitrification fueled by the DOC from the barrier may be contributing to the lower NO3 --N concentrations. Monitoring will continue at the site to determine the longer-term water quality trends. More research should be conducted to evaluate the applicability of permeable barriers as a best management practice for non-point sources of pollution in nutrient sensitive areas. © 2015 Charles Humphrey, Sushama Pradhan, Eban Bean, Michael O’Driscoll and Guy Iverson.
... The red seaweed Porphyra yezoensis, grown on a large seaweed farm (300 ha) in China, removed approximately 50 kg per ha of nitrogen annually (He et al., 2008). Bowen and Valiela (2004) examined a potential bio-extraction of N via harvesting naturally abundant macroalgae. If the mean annual biomass of the standing stock of seaweed was harvested from Waquoit Bay, an estimated 15-66 kg N would be removed per hectare each year. ...
Article
Nutrient bioextraction using Gracilaria tikvahiae McLachlan was tested at two sites: one off Fairfield, CT (LIS), and the other at the mouth of the Bronx River Estuary (BRE), during the summer and fall of 2011 and 2012. The estimates of nitrogen (N) removal by Gracilaria over a 90-day growing season were up to 28 and 94 kg N ha −1 at the LIS and BRE sites, respectively. In July 2012, Gracilaria grew up to 16.5% day −1 at BRE and 4.8% day −1 at the LIS site. Tissue N contents at the same periods were 3.7% (BRE) and 1.5% (LIS), respectively. These results demonstrate rapid assimilation of nutrients fueling the growth of new Gracilaria tissue at the BRE site, while nutrients appeared to limit growth at the LIS site during the summer months. The estimated C removal by Gracilaria at the BRE and LIS sites were up to 300 kg ha −1 (LIS) and 727 kg ha −1 (BRE), respectively. The potential economic values of N and C sequestration for the period examined in this study were as high as $311 (LIS) and $940 ha −1 (BRE) for N, and $5.51 (LIS) and $13.32 ha −1 (BRE) for C if seaweed aquaculture would be included in Connecticut's Nitrogen Trading Program. This represents a potential additional economic incentive for seaweed growers, beyond the direct value of seaweed products. The findings in this study showed that seaweed (Gracilaria) aquaculture can be a useful technique for nutrient bioextraction in urbanized coastal waters, such as the estuaries of New York City (BRE) and Long Island Sound.
... The red seaweed Porphyra yezoensis, grown on a large seaweed farm (300 ha) in China, removed approximately 50 kg per ha of nitrogen annually (He et al., 2008). Bowen and Valiela (2004) examined a potential bio-extraction of N via harvesting naturally abundant macroalgae. If the mean annual biomass of the standing stock of seaweed was harvested from Waquoit Bay, an estimated 15-66 kg N would be removed per hectare each year. ...
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Seagrasses provide important ecological services that directly or indirectly benefit human well-being and the environment. Excess nitrogen inputs are a major cause of eelgrass loss in the marine environment. Here we describe the results of a study aimed at quantifying the extent of eelgrass as a function of predicted watershed-derived nitrogen loading for small-to-medium-sized shallow estuaries in New England. Findings confirm that reduced extent of eelgrass corresponds to increased loading of nitrogen to this class of estuary. At lower levels of nitrogen loading (≤50 Kg ha−1 yr−1), eelgrass extent is variable and is likely controlled by other ecosystem factors unrelated to water quality. At higher loading rates, eelgrass coverage decreases markedly, with essentially no eelgrass at loading levels ≥100 Kg ha−1 yr−1.
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Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH4-N), nitrate (NO3-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH4-N (57–62% or 1.44 × 105–2.32 × 105 kg yr−1) followed by the diversion. The diversion was the greatest source of NO3-N (67–83%, 7.78 × 105–1.64 × 106 kg yr−1) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 105–2.32 × 105 kg yr−1). Annual loading rates of NH4-N and NO3-N were 0.17–0.27 and 1.2–2.3 g N m−2 yr−1, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.
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The effects of nitrogen (N) addition on microbial biomass, bacterial abundance, and community composition in sediment colonized by Suaeda heteroptera were examined by chloroform fumigation extraction method, real-time quantitative polymerase chain reaction, and denaturing gradient gel electrophoresis (DGGE) in a salt marsh located in Shuangtai Estuary, China. The sediment samples were collected from plots treated with different amounts of a single N fertilizer (urea supplied at 0.1, 0.2, 0.4 and 0.8 g/kg (nitrogen content in sediment) and different forms of N fertilizers (urea, (NH4)2SO4, and NH4NO3, each supplied at 0.2 g/kg (calculated by nitrogen). The fertilizers were applied 1–4 times during the plant-growing season in May, July, August, and September of 2013. Untreated plots were included as a control. The results showed that both the amount and form of N positively influenced microbial biomass carbon, microbial biomass nitrogen, and bacterial abundance. The DGGE profiles revealed that the bacterial community composition was also affected by the amount and form of N. Thus, our findings indicate that short-term N amendment increases microbial biomass and bacterial abundance, and alters the structure of bacterial community.
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Eutrophication of estuaries is an increasing global concern that requires development of new tools to identify causes, quantify conditions, and propose management options that address this environmental problem. Since eutrophication is often associated with increased inputs of land-derived nitrogen to estuaries, we developed NLOAD, a user-friendly, web-based tool that brings together six different published models that predict nitrogen loading to estuaries and two models that estimate nitrogen concentrations in coastal waters. Here we describe each of the models, demonstrate how NLOAD is designed to function, and then use the models in NLOAD to predict nitrogen loads to Barnegat Bay, New Jersey (USA). The four models that we used to estimate nitrogen loads to Barnegat Bay, when adjusted, all had similar results that matched well with measured values and indicated that Barnegat Bay receives roughly 26 kg N-ha(-1).yr(-1). Atmospheric deposition was the dominant source of nitrogen to Barnegat Bay, followed by fertilizer nitrogen. Wastewater in Barnegat Bay is diverted to an offshore outfall and contributes no nitrogen to the system. The NLOAD tool has an additional feature that allows managers to assess the effectiveness of a variety of management options to reduce nitrogen loads. We demonstrate this feature of NLOAD through simulations in which fertilizer inputs to the Barnegat Bay watershed are reduced. Even modest cutbacks in the use of fertilizers on agricultural fields and lawns can be shown to reduce the amount of N entering Barnegat Bay.
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Non-point source eutrophication of coastal waters is a significant problem that may be exacerbated locally by effluent from aquaculture operations. Porphyra spp. grow and assimilate nutrients rapidly, making them good candidates for eutrophication abatement via systems of integrated aquaculture. I summarize our work examining the bioremediatory performance (growth rate, nutrient assimilation, tissue N and pigment content) of four U.S. and three Asian Porphyra species as functions of N concentration and source (nitrate vs. ammonium). The Northeast U.S. species P. amplissima is the best performing local bioremediator (maximum growth rate and tissue N=24% d-1, 5.2% DW, respectively), comparing well with P. yezoensis, an economically important species in Asia. When tissue remained non-reproductive, P. amplissima growing in 300 μM ammonium removed 99–100% of N but only about 50% of P (fed 10:1 molar N:P ratio). We have begun investigating the relationship between stocking density and yield, and will begin demonstration scale tests of the mesoscale system.
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The flux of terrestrially derived pathogens to coastal waters presents a significant health risk to marine wildlife, as well as to humans who utilize the nearshore for recreation and seafood harvest. Anthropogenic changes in natural habitats may result in increased transmission of zoonotic pathogens to coastal waters. The objective of our work was to evaluate how human-caused alterations of coastal landscapes in California affect the transport of Toxoplasma gondii to estuarine waters. Toxoplasma gondii is a protozoan parasite that is excreted in the feces of infected felids and is thought to reach coastal waters in contaminated runoff. This zoonotic pathogen causes waterborne toxoplasmosis in humans and is a significant cause of death in threatened California sea otters. Surrogate particles that mimic the behavior of T. gondii oocysts in water were released in transport studies to evaluate if the loss of estuarine wetlands is contributing to an increased flux of oocysts into coastal waters. Compared to vegetated sites, more surrogates were recovered from unvegetated mudflat habitats, which represent degraded wetlands. Specifically, in Elkhorn Slough, where a large proportion of otters are infected with T. gondii, erosion of 36% of vegetated wetlands to mudflats may increase the flux of oocysts by more than 2 orders of magnitude. Total degradation of wetlands may result in increased Toxoplasma transport of 6 orders of magnitude or more. Destruction of wetland habitats along central coastal California may thus facilitate pathogen pollution in coastal waters with detrimental health impacts to wildlife and humans.
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We developed a simple model that related NO3 export to point-source N loading and nonpoint source N loads from chemical fertilizers and NO(y) deposition and tested it at the global scale using data from 35 large rivers with a global distribution. The model explained well (r2 > 0.8) the nearly 1000-fold variation in NO3 export from different regions of the world. The model suggests that human activity is the dominant control of NO3 export even though less than 20 of the 100 Tg N yr-1 added to land in fertilizer and NO(y) deposition is at present exported from rivers as NO3. Watershed export to rivers may increase in the future due to either increased loads to the watershed or decreased watershed retention. Simple models, coupled with continued measurements of NO3 in rivers, will be of use in interpreting these regional changes.
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We measured annual discharges of water, sediments, and nutrients from 17 Chesapeake Bay watersheds with differing proportions of agricultural lands on the inner, central, and outer Coastal Plain. In all regions of the Coastal Plain, the flow-weighted mean concentrations of N species in watershed discharge increased as the proportion of cropland in the watershed increased. In contrast, the concentrations of P species did not correlate with any land use. Instead, P concentrations correlated with the concentration of suspended particles, which differed greatly among watersheds in different regions of the Coastal Plain. Consequently, the ratio of N/P in discharges differed widely among watersheds, potentially affecting N or P limitation of phytoplankton growth in the receiving waters. Concentrations of dissolved silicate, organic C, pH, and alkalinity in discharges did not differ greatly among watersheds or correlate with land rise. Nitrogen discharge correlated with net anthropogenic inputs of N to the watershed, but usually less than one-third of the net anthropogenic inputs were discharged.
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Though it is well known that the world's coastlines are heavily populated, the combined implications of population growth and climate change are still subject to debate. Models of hazard impact, adaptation, and vulnerability stress the importance of understanding both exposure and adaptive capacity of the threatened systems [e.g.,Smit et al., 2001]. Combining geophysical and socio-economic data sets can greatly improve our understanding of exposure at a range of scales from local to global.Here we estimate an upper bound on the global exposure to coastal hazards based on 1990 population distribution. The focus is on exposure to natural hazards, but these estimates also provide an indication of the direct human pressure on the coastal zone. Data from 1990 were used, as this global population distribution was the most robust currently available.
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Results from four intensive site-level manipulations and one extensive field survey in northern temperate and boreal forests show a consistent set of responses to chronic N additions. These include 1) initial and often large increase in net N mineralization followed by decreases, 2) increases in net nitrification. 3) increases in N concentration in foliage, and 4) decreased MgN and CaAl ratios, and declining tree growth and vigor in all evergreen stands. These results are synthesized into a set of proposed summary relationships that define the temporal pattern of responses of N-limited systems to N additions.
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We evaluated the accuracy of six watershed models of nitrogen export in streams (kg km2 yr–1) developed for use in large watersheds and representing various empirical and quasi-empirical approaches described in the literature. These models differ in their methods of calibration and have varying levels of spatial resolution and process complexity, which potentially affect the accuracy (bias and precision) of the model predictions of nitrogen export and source contributions to export. Using stream monitoring data and detailed estimates of the natural and cultural sources of nitrogen for 16 watersheds in the northeastern United States (drainage sizes = 475 to 70,000 km2), we assessed the accuracy of the model predictions of total nitrogen and nitrate-nitrogen export. The model validation included the use of an error modeling technique to identify biases caused by model deficiencies in quantifying nitrogen sources and biogeochemical processes affecting the transport of nitrogen in watersheds. Most models predicted stream nitrogen export to within 50% of the measured export in a majority of the watersheds. Prediction errors were negatively correlated with cultivated land area, indicating that the watershed models tended to over predict export in less agricultural and more forested watersheds and under predict in more agricultural basins. The magnitude of these biases differed appreciably among the models. Those models having more detailed descriptions of nitrogen sources, land and water attenuation of nitrogen, and water flow paths were found to have considerably lower bias and higher precision in their predictions of nitrogen export.
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A number of local, regional, state, and federal programs are in place that strive to protect and restore coastal waters and habitats, and which specifically address eutrophication and nutrient over-enrichment. There are, however, no easily implemented and reliable methods or sources of data and information for citizens, coastal managers, elected officials, and agency staff who are responsible for managing a coastal area to determine sources of nutrients and potential impacts to coastal waters. Coordination among federal and local agencies remains inadequate. In the few examples of successful coastal nutrient management programs, effective nutrient management strategies are often partnerships of national, regional, and local efforts. The recent National Research Council (2000) examination of issues and management options calls for development of a National Coastal Nutrient Management Strategy, coordinated between national, state and local programs, academia, and the private sector. The proposed National Coastal Nutrient Management Strategy includes recommendations for local programs to consider in developing an effective nutrient management strategy, such as setting goals for restoration, determining nutrient reductions needed to meet goals, and monitoring results. The proposed strategy also identifies priority actions which federal programs should consider, including identifying gaps and overlaps in existing and proposed national programs for all aspects of nutrient over-enrichment; increasing accessibility to data, information and expertise on nutrient over-enrichment causes, effects, and management options; and setting clear guidelines for nutrient loads. A nationally consistent monitoring program and targeted research, specifically for atmospheric deposition, seasonal variability of nitrogen and phosphorus enrichment effects, the role of specific nutrients in the occurrence of harmful algal blooms, and economic impacts of nutrient over-enrichment were also identified as priority needs.
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This valuable reference delineates the ground water quality concerns associated with the planning and usage of septic tank systems. Septic tank systems represent a significant source of ground water pollution in the United States. Since many existing systems are exceeding their design life by several-fold, the usage of synthetic organic chemicals in the household and for system cleaning is increasing, and larger-scale systems are being designed and used.
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The abstract for this document is available on CSA Illumina.To view the Abstract, click the Abstract button above the document title.
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We have developed a dynamic nitrogen loading model (NLM) that incorporates temporal and spatial trends in land use with a three-dimensional ground water model. In conjunction with historical patterns of land use in the Waquoit Bay (USA) watershed, we have modified an existing steady-state watershed NLM to estimate historical and future rates of total dissolved nitrogen (TDN) to the coastal margins of Waquoit Bay and its subestuaries. The model simulations indicated a significant increase in nitrogen loading to these systems in recent decades. We estimated that the TDN loading rate to Waquoit Bay increased from approximately 5000 to 23 000 kg yr-1 (0.8 to 3.7 g N m-2 yr-1) from 1930 to 1990. We also compared the dynamic model with steady-state simulations where the lag effect of ground water travel time was not considered. These results indicate occasional significant differences (up to 37%) between the two modeling methods, especially between 1950 and 1990, when large areas of naturally vegetated and agricultural land witluin the watershed were converted to unsewered residential housing. Although all subestuaries experienced similar temporal trends in nitrogen load, heterogeneity in the timing, source, and magnitude indicates that these factors are dependent upon watershed size, shape, and spatio-temporal trends in land use.
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In this paper we develop a model to estimate nitrogen loading to watersheds and receiving waters, and then apply the model to gain insight about sources, losses, and transport of nitrogen in groundwater moving through a coastal watershed. The model is developed from data of the Waquoit Bay Land Margin Ecosystems Research project (WBLMER), and from syntheses of published information. The WBLMER nitrogen loading model first estimates inputs by atmospheric deposition, fertilizer use, and wastewater to surfaces of the major types of land use (natural vegetation, turf, agricultural land, residential areas, and impervious surfaces) within the landscape. Then, the model estimates losses of nitrogen in the various compartments of the watershed ecosystem. For atmospheric and fertilizer nitrogen, the model allows losses in vegetation and soils, in the vadose zone, and in the aquifer. For wastewater nitrogen, the model allows losses in septic systems and effluent plumes, and it adds further losses that occur during diffuse transport within aquifers. The calculation of losses is done separately for each major type of land cover, because the processes and loss rates involved differ for different tesserae of the land cover mosaic. If groundwater flows into a freshwater body, the model adds a loss of nitrogen for traversing the freshwater body and then subjects the surviving nitrogen to losses in the aquifer. The WBLMER model is developed for Waquoit Bay, but with inputs for local conditions it is applicable to other rural to suburban watersheds underlain by unconsolidated sandy sediments. Model calculations suggest that the atmosphere contributes 56%, fertilizer 14%, and wastewater 27% of the nitrogen delivered to the surface of the watershed of Waquoit Bay. Losses within the watershed amount to 89% of atmospheric nitrogen, 79% of fertilizer nitrogen, and 65% of wastewater nitrogen. The net result of inputs to the watershed surface and losses within the watershed is that wastewater becomes the largest source (48%) of nitrogen loads to receiving estuaries, followed by atmospheric deposition (30%) and fertilizer use (15%). The nitrogen load to estuaries of Waquoit Bay is transported primarily through land parcels covered by residential areas (39%, mainly via wastewater), natural vegetation (21%, by atmospheric deposition), and turf (16%, by atmospheric deposition and fertilizers). Other land covers were involved in lesser throughputs of nitrogen. The model results have implications for management of coastal landscapes and water quality. Most attention should be given to wastewater disposal within the watershed, particularly within 200 m of the shore. Rules regarding setbacks of septic system location relative to shore and nitrogen retention ability of septic systems, will be useful in control of wastewater nitrogen loading. Installation of multiple conventional leaching fields or septic systems in high-flow parcels could be one way to increase nitrogen retention. Control of fertilizer use can help to a modest degree, particularly for optional uses such as lawns situated near shore. Conservation of parcels of accreting natural vegetation should be given high priority, because these environments effectively intercept atmospheric deposition. Areas upgradient from freshwater bodies should be given low priority in plans to control nitrogen loading, because ponds intercept much of the nitrogen transported from upgradient.
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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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A three-dimensional nonlinear numerical hydrodynamic model using Legendre polynomials to represent the vertical structure of the horizontal currents has been used to study the tidally induced residual flows in the Gulf of Maine–Georges Bank study region using a 6.25 km square grid. Tidal elevations in terms of the M2 phase and amplitude along the open boundaries are specified using Schwiderski's deep ocean tidal model. The model predicts strong clockwise circulation gyres around Georges Bank and Nantucket Shoals with a weak gyre around Browns Bank. Strong inflow to the Gulf of Maine is predicted near the Southwestern tip of Nova Scotia. These results are in good agreement with recent model predictions of Greenberg.
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Historical changes in land use on coastal watersheds have increased rates of land-derived nitrogen loading to estuaries and altered their biogeochemistry and food webs. We used information on human populations and land uses within the watershed of Waquoit Bay, Cape Cod, Massachusetts, U.S.A., to model how nitrogen loads derived from atmospheric deposition, fertilizer use, and wastewater disposal have changed since the 1930s. Nitrogen loading into Waquoit Bay more than doubled between 1938 and 1990. The predominant source of nitrogen added to the bay changed from atmospheric deposition to wastewater disposal during the 1980s, reflecting the increasing urbanization of Cape Cod. Larger nitrogen loads increased nitrogen concentrations in the water, altering the assemblage of primary producers and resulting in eutrophication of the estuary. Biomass of phytoplankton and macroalgae increased, and areal cover of eelgrass (Zostera marina) decreased, with increasing nitrogen load. An increase in nitrogen load from 15 to 30 kg N.ha(-1).year(-1) virtually eliminated eelgrass meadows. Land-use changes prompted by urban sprawl can therefore be linked to marked changes in water quality and eutrophication of receiving waters.
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We followed the movements of 15N-labelled nitrate additions into biomass and soil pools of experimental plots (15×15 m each) in a mid-successional beech-maple-birch-spruce forest in order to identify sinks for nitrate inputs to a forest ecosystem. Replicate plots (n=3) were spray-irrigated with either 28 or 56 kg N ha-1 year-1 using 15N-labelled nitric acid solutions (d15N = 344‰ ) during four successive growing seasons (April–October). The 15N contents of foliage, bolewood, forests floor and mineral soil (0–5 cm) increased during the course of treatments. Mass balance calculations showed that one-fourth to one-third of the nitrate applied to forest plots was assimilated into and retained by above ground plant tissues and surface soil horizons at both rates of nitrate application. Plant and microbial assimilation were of approximately equal importance in retaining nitrate additions to this forest. Nitrate use among tree species varied, however, with red spruce showing lower rates of nitrate assimilation into foliage and bolewood than American beech and other deciduous species.
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Human activities have roughly doubled the amount of reactive N that enters the element's biospheric cycle. Crop production is by far the single largest cause of this anthropogenic alteration. Inorganic fertilizers now provide 80 TgNyr-1 (Tg=1012g), managed (symbiotic) biofixation adds about 20 TgNyr-1, and between 28 and 36 TgNyr-1 are recycled in organic wastes. Anthropogenic inputs (including N in seeds and irrigation water) now supply about 85% of 170 (151-186) Tg N reaching the world's cropland every year. About half of this input, 85 TgNyr-1, is taken up by harvested crops and their residues. Quantification of N losses from crop fields is beset by major uncertainties. Losses to the atmosphere (denitrification and volatilization) amount to 26-60 TgNyr-1, while waters receive (from leaching and erosion) 32-45 TgNyr-1. These N losses are the major reason behind the growing concerns about the enrichment of the biosphere with reactive N. The best evidence suggests that in spite of some significant local and regional losses, the world's agricultural land accumulates N. The addition of 3-4 billion people before the year 2050 will require further substantial increases of N input in cropping, but a large share of this demand can come from improved efficiency of N fertilizer use.
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Macroalgal blooms arc produced by nutrient enrichment of estuaries in which the sea floor lies within the photic zone. We review fcaturcs of macroalgal blooms pointed out in recent literature and summarize work done in the Waquoit Bay Land Margin Ecosystems Research project which suggests that nutrient loads, water residcncc times, presence of fringing salt marshes, and grazing affect macroalgal blooms. Increases in nitrogen supply raise macroalgal N uptake rates, N contents of tissues, photosynthesis-irradiance curves and P,,,.,, and accelerate growth of fronds. The resulting increase in macroalgal biomass is the macroalgal bloom, which can displace other estuarine producers, Fringing marshes and brief water residence impair the intensity of macroalgal blooms. Grazing pressure may control blooms of palatable macroalgac, but only at lower N loading rates. Macroalgal blooms end when growth of the phytoplankton attenuates irradiation reaching the bottom. In cstuarics with brief water rcsidencc times, phytoplankton may not have enough time to grow and shade macrophytcs. High phytoplankton division rates achieved at high nutrient concentrations may compensate for the brief time to divide before cells arc transported out of the estuary. Increased N loads and associated macroalgal blooms pervasively and fundamentally alter estuarinc ecosystems. Macroalgae intercept nutrients regenerated from sediments and thus uncoupIe biogeochemical sedimentary cycles from those in the water column. Macroalgae take up so much N that water quality seen:? high even where N loads are high. Macroalgal C moves more readily through microbial and consumer food webs than C derived from seagrasscs that were replaced by macroalgae. Macroalgae dominate 0, profiles of the water columns of shallow estuaries and thus alter the biogeochemistry of the sediments. Marc frequent hypoxia and habitat changes associated with macroalgal blooms also changes the abundance of bcnthic fauna in affected estuaries. Approaches to rcmediation of the many pervasive cffccts of macroalgal blooms riced to include interception of nutrients at their watcrshcd sources and perhaps removal by harvest of macroalgae or by increased flushing. Al- though we have much knowledge of macroalgal dynamics, all such management initiatives will require additional information.
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Sustainable coastal management requires that the goals and means of management be made operational and specific. We use Waquoit Bay, Massachusetts, as a case study, to suggest a decision-making process that brings updated scientific results forward while incorporating stakeholder concerns. Land-derived nitrogen loading is the major agent of change for receiving estuaries in the Waquoit Bay estuarine complex, so control of nitrogen loading rates is a principal goal of land management plans. We can establish the relationships of land use pattern to nitrogen loading rates, and of loading rates to mean annual concentrations of nitrogen in the estuaries. The latter, in turn, can be related quantitatively to mean annual production and biomass of phytoplankton, macroalgae, and eel-grass. We propose that phytoplankton, macroalgal, and eelgrass production and biomass are suitable end point measures that can be made meaningful to stakeholders. We define the relationship of agent of change vs. end point measure, and then have policy makers and stakeholders decide which critical end point is desirable or acceptable for the selected end point measures. Thus, science results and stakeholder opinion are merged to establish management goals. Having chosen a desired critical end point, we can use nitrogen loading models to assess the degree to which different management options can alter nitrogen loading rates to levels that meet the agreed-upon management goals. These modeled simulations will identify the effects on loading rates from each management action and, hence, permit an assessment of a suite of management actions that can be used to meet the management goals. These procedures incorporate ecological knowledge with cultural, political, and economical imperatives and force identification of what is acceptable as an end result. These strategies furnish one way to design reasonable, and ecologically and socially sustainable plans for the inevitable use and management of coastal watersheds.
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The high salt marshes of New England have evolved in response to sea-level rises through accretion of sediments entrapped by marsh vegetation. Early theories of marsh development are traced and are reconciled in Redfield's synthesis accounting for marsh growth by aggradation over sand and mud flats as well as by accretion on existing marsh surfaces. The shape and appearance of high marshes result from unique, complex interactions of local topography and bathymetry, sea-level rise, tides, sediment supply and vegetation. These factors, particularly the major influences of tides and short-term changes in sea-level, are incorporated in short-term processes that define and mold the ecology of the high marsh. Short- and long-term mechanisms have produced approximate zonation of vegetation in the high marsh. High marshes are contrasted to Spartina-dominated low marsh in terms of plant and animal species and the relative importance of the dynamics of production, export, decomposition, and accumulation of materials in the sediments. High marshes have been subjected to man's activities since earliest English settlement. This history of New Englanders' impact on this community is traced from their use of marshes as hay fields to depositories of pollutants. Habitat management considerations today include mosquito control and sewage sludge treatment. 154 refs., 29 figs., 14 tabs.
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Submerged vegetation respond to increased nutrient loading through a shift from slow-growing seagrasses and large macroalgae to fast-growing macroalgae, and the ultimate dominance of phytoplankton at high nutrient loadings. This shift reflects a change from nutrient to light limitation along the eutrophication gradient. Slow-growing seagrasses and large macroalgae are good competitors when nutrients are limiting because they have relatively low nutrient requirements, are able of efficient internal nutrient recycling, and can access the elevated nutrient pools in the sediment. Fast-growing macroalgae and phytoplankton are superior competitors when light is limiting because they are positioned closer to the water surface, and capture and use light more efficiently. The important ecosystem consequences of altered nutrient regimes derive from the shift in dominant vegetation types. Slow-growing seagrasses and large macroalgae are longevous, decompose slowly, and experience only moderate grazing losses, whereas the production of fast growing macroalgae and phytoplankton is transferred faster to heterotrophs, through increased grazing and decomposition rates. Recovery of submerged vegetation following nutrient reduction plans is a very slow process, which involves the replacement of fast-growing for slow-growing plants. Simulation models predict recovery times to oscillate between a few years for macroalgae and fast-growing seagrasses to centuries for slow-growing seagrasses following nutrient reduction plans.
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Planners concerned with water resource protection in urbanizing areas must deal with the adverse impacts of polluted runoff. Impervious surface coverage is a quantifiable land-use indicator that correlates closely with these impacts. Once the role and distribution of impervious coverage are understood, a wide range of strategies to reduce impervious surfaces and their impacts on water resources can be applied to community planning, site-level planning and design, and land use regulation. These strategies complement many current trends in planning, zoning, and landscape design that go beyond water pollution concerns to address the quality of life in a community.
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Recently compiled data document a 3−8-fold increase in nitrate fluxes from 10 watersheds in the Northeast United States since the early 1900s. During this period, nitrogen oxide emissions from combustion sources have increased about 5-fold. For 17 large watersheds with relatively minor agricultural or urban influences, riverine nitrogen fluxes from 1990 to 1993 were highly correlated with atmospheric deposition onto their landscapes and also with nitrogen oxide emissions into their airsheds. These relationships provided two methods of estimating riverine nitrogen export directly from either deposition or emission fluxes. For 10 benchmark watersheds with good historical data, about 36−80% of the riverine total nitrogen export, with an average of 64%, was derived directly or indirectly from nitrogen oxide emissions. Atmospheric deposition of nitrogen represented only about 25% of the airshed emissions with the remaining 75% transported out of the airshed. Nitrogen is the element most responsible for eutrophication in coastal waters of this region. Our analysis suggests a strong linkage between the increase in cultural eutrophication of the coastal waters of the Northeast United States and the increase in nitrogen oxide emissions from fossil fuel combustion.
Article
Human activities on coastal watersheds provide the major sources of nutrients entering shallow coastal ecosystems. Nutrient loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. To investigate this coupling of land to marine systems, we are studying a series of subwatersheds of Waquoit Bay that differ in degree of urbanization and hence are exposed to widely different nutrient loading rates. The subwatersheds differ in the number of septic tanks and the relative acreage of forests. In the area of our study, groundwater is the major mechanism that transports nutrients to coastal waters. Although there is some attenuation of nutrient concentrations within the aquifer or at the sediment-water interface, in urbanized areas there are significant increases in the nutrient content of groundwater arriving at the shore’s edge. The groundwater seeps or flows through the sediment-water boundary, and sufficient groundwater-borne nutrients (nitrogen in particular) traverse the sediment-water boundary to cause significant changes in the aquatic ecosystem. These loading-dependent alterations include increased nutrients in water, greater primary production by phytoplankton, and increased macroaglal biomass and growth (mediated by a suite of physiological responses to abundance of nutrients). The increased macroalgal biomass dominates the bay ecosystem through second- or third-order effects such as alterations of nutrient status of water columns and increasing frequency of anoxic events. The increases in seaweeds have decreased the areas covered by eelgrass habitats. The change in habitat type, plus the increased frequency of anoxic events, change the composition of the benthic fauna. The data make evident the importance of bottom-up control in shallow coastal food webs. The coupling of land to sea by groundwater-borne nutrient transport is mediated by a complex series of steps; the cascade of processes make it unlikely to find a one-to-one relation between land use and conditions in the aquatic ecosystem. Study of the process and synthesis by appropriate models may provide a way to deal with the complexities of the coupling.
Article
World-wide eutrophication of estuaries has made accurate estimation ofland-derived nitrogen loads an important priority. In this paper we verifypredictions of nitrogen loads made by the Waquoit Bay Nitrogen LoadingModel (NLM). NLM is appropriate for watersheds with mixes of forested,agricultural, and residential land uses, and underlain by coarseunconsolidated sediments. NLM tracks the fate of nitrogen inputs byatmospheric deposition, fertilizer use, and wastewater disposal, and assignslosses of nitrogen from each source as the nitrogen is transported throughthe land use mosaic on the watershed surface, then through the underlyingsoils, vadose zones, and aquifers. We verified predictions of nitrogen loads by NLM in two independent ways.First, we compared NLM predictions to measured nitrogen loads in differentsubestuaries in the Waquoit Bay estuarine system. Nitrogen loads predictedby NLM were statistically indistinguishable from field-measured nitrogenloading rates. The fit of model predictions to measurements remained goodacross the wide range of nitrogen loads, and across a broad range in size(10–10,000 ha) of land parcels. NLM predictions were most precise whenspecific parcels were larger than 200 ha, and within factors of 2 for smallerparcels. Second, we used NLM to predict the percentage of nitrogen loads toestuaries contributed by wastewater, and compared this prediction to theδ15N signature distinguishable from N derived fromatmospheric or fertilizer sources. The greater the contribution ofwastewater, the heavier the δ15N value in groundwater. Thesignificant linear relation between NLM predictions of percent wastewatercontributions and stable isotopic signature corroborated the conclusionthat model outputs provide a good match to empirical measurements. Thegood agreement obtained in both verification exercises suggests that NLMis an useful tool to address basic and applied questions about how land usepatterns alter the fate of nitrogen traversing land ecosystems, and thatNLM provides verified estimates of the land-derived nitrogen exports thattransform receiving aquatic ecosystems.
Article
Seagrass meadows within estuaries are highly sensitive to increased supplies of nitrogen (N). The urbanization of coastal watersheds increases the delivery of N to estuaries, threatening seagrass habitats; both seagrass production per unit area and the area of seagrass meadows diminish as land-derived N loads increase. The damaging effects of land-derived N loads may be lessened where there are fringes of coastal wetlands interposed between land and seagrass meadows. Data compiled from the literature showed that production per unit area by seagrasses increased and losses of seagrass habitat were lower in estuaries with relatively larger areas of fringing wetlands. Denitrification and the burial of land-derived N within fringe wetlands may be sufficient to protect N-sensitive seagrass habitats from the detrimental effects of land-derived N. The protection furnished by fringing wetlands may be overwhelmed by increases in anthropogenic N loads in excess of 20–100 kg N ha−1 y−1. The relationships of land-derived N loadings, fringing coastal wetlands, and seagrass meadows demonstrate that different units of the landscape mosaic found in coastal zones do not exist as separate units, but instead are coupled and uncoupled by biogeochemical transformations and transport among environments.
Article
The sewage treatment plant (STP) at La Parguera, on the southwest coast of Puerto Rico, discharges an average of 228,000 dm3 of secondary sewage effluents per day into percolation ponds located at the landward margin of the coastal mangrove fringe. Effluents flowing from the STP percolation ponds to the adjacent mangrove fringe typically exhibited nitrate levels between 0.2 mM and 1.0 mM. Experimental determination of actual and potential denitrification using acetylene block and substrate disappearance techniques indicate that mangrove sediment microbial communities are capable of depurating 10 to 15 times the nitrate added in the STP effluent. Plots of porewater salinities vs nitrate concentrations show exponential decay of nitrate concentration. Our observations confirm the potential of mangrove sediment-microbial communities for nitrate depuration of secondary sewage effluents.
Article
A simple model of annual average response of an estuary to mean nitrogen loading rate and freshwater residence time was developed and tested. It uses nitrogen inputs from land, deposition from the atmosphere, and first-order calculations of internal loss rate and net export to perform a steady-state analysis over a yearly cycle. The model calculates the fraction of total nitrogen input from land and the atmosphere that is exported and the fraction that is denitrified or lost to other processes within the estuary. The model was tested against data from the literature for 11 North American and European estuaries having a wide range of physical characteristics, nitrogen loading rates, and geographical and climatic settings. The model shows that the fraction of nitrogen entering an estuary that is exported or denitrified can be predicted from the freshwater residence time. The first-order rate constant for nitrogen loss within an estuary, as a fraction of total nitrogen in the water column, is 0.30 mo−1. Denitrification typically accounts for 69–75% of the total annual net nitrogen removal from the water column by processes within the estuary. The model makes explicit the dependence of nitrogen concentration in the water column on the loading rate of nitrogen, water residence time, estuary volume, and the rate constant for loss within the estuary.
Article
Nutrient excretion rates and the annual contribution of P from the feces of the gulls Larus argentatus and L. marinus (and of N from L. argentatus) to the nutrient budget of Gull Pond (Wellfleet), a soft water seepage lake, have been estimated. Intensive year-round gull counts by species were combined with determinations of defecation rate and the nutrient content of feces to quantitatively assess the P loading rates associated with regular gull use of this coastal pond on a seasonal and annual basis. Total P loading from gulls was estimated to be 52 kg yr–1, with 17 kg from L. argentatus and 35 kg from L. marinus, resulting from about 5.0 106 h yr–1 and 1.7 106 h yr–1 of pond use. This compares with P loading estimates of 67 kg yr–1 from upgradient septic systems, 2 kg yr–1 from precipitation and 3 kg yr–1 from unpolluted ground water. Fifty-six percent of annual gull P loading was associated with migratory activity in late fall. Estimated annual N loading by L. argentatus was 14 kg TKN, 206 g NO3-N, and 1.85 g g NH3-N.
Article
An assessment of developing eutrophic conditions in small temperate lagoons along the coast of Rhode Island suggests that in such shallow, macrophyte based systems the response to nutrient enrichment differs from that described for plankton based systems. The nitrogen loadings per unit area of the salt ponds are 240–770 mmol N per m2 per year. Instead of the high nutrient concentrations, increased phytoplankton biomass and turbidity, leading to eventual loss of benthic macrophytes described for such systems as the Chesapeake, Patuxent and Appalachicola Bay, nutrient enrichment of the Rhode Island lagoons has led to increased growth of marine macroalgae. The increased macroalgal growth appears to alter the benthic habitat and a shift from a grazing to detrital food chain appears to be impacting important shellfisheries. As more extensive areas of organic sediments develop, geochemical cycling changes, resulting in higher rates of nitrogen remineralization and accelerated eutrophication. The major sources of nitrogen inputs to the salt ponds have been identified and a series of management initiatives have been designed to limit inputs from present and potential development within the watersheds of the lagoons.
Article
We reconstructed the historical trends in atmospheric deposition of nitrogen to Cape Cod, Massachusetts, from 1910 to 1995 by compiling data from literature sources, and adjusting the data for geographical and methodological differences. The reconstructed data suggest that NO3-N wet deposition to this region increased from a low of 0.9 kg N ha−1 yr−1 in 1925 to a high of approximately 4 kg N ha−1 yr−1 around 1980. The trend in NO3-N deposition has remained since the early 1980s at around 3.6 kg N ha−1 yr−1. In contrast, NH4-N wet deposition decreased from more than 4 kg N ha−1 yr−1 in the mid 1920s to about 1.5 kg N ha−1 yr−1 from the late-1940s until today. Emissions of NOx-N in the Cape Cod airshed increased at a rate of 2.1 kg N ha−1 per decade since 1910, a rate that is an order of magnitude higher than NO3-N deposition. Estimates of NH3 emissions to the northeast United States and Canada have decreased slightly throughout the century, but the decrease in reconstructed N-NH4+ deposition rates does not parallel emissions estimates. The trend in reconstructed total nitrogen deposition suggests an overall increase through the century at a rate of 0.26 kg N ha−1 per decade. This overall increase in deposition may expose coastal forests to rates of nitrogen addition that, if exceeded, could induce nitrogen saturation and increase nitrogen loads to adjoining estuaries.