A comparative analysis of eutrophication patterns in a temperate coastal lagoon

Estuaries and Coasts (Impact Factor: 2.25). 01/1996; 19(2):408-421. DOI: 10.2307/1352459

ABSTRACT The coastal bays and lagoons of Maryland extend the full length of the state's Atlantic coast and compose a substantial ecosystem
at the land-sea margin that is characterized by shallow depth, a well-mixed water column, slow exchange with the coastal ocean,
and minimal freshwater input from the land. For at least 25 years, various types of measurements have been made intermittently
in these systems, but almost no effort has been made to determine if water quality or habitat conditions have changed over
the years or if distinctive spatial gradients in these features have developed in response to changing land uses. The purpose
of this work was to examine this fragmented database and determine if such patterns have emerged and how they may be related
to land uses. Turbidity, dissolved inorganic phosphate, algal biomass, and primary production rates in most areas of the coastal
bays followed a regular seasonal pattern, which was well correlated with water temperature. Nitrate concentrations were low
(<5 μM), and only modestly higher in tributary creeks (<20 μM). Additionally, there was little indication of the spring bloom
typical of river-dominated systems. There does appear to be a strong spatial gradient in water quality conditions (more eutrophic
in the upper bays, especially in tributary creeks). Comparisons of water quality data collected between 1970 and 1991 indicate
little temporal change in most areas and some small improvements in a few areas, probably related to decreases in point-source
discharges. Seagrass communities were once extensive in these systems but at present are restricted to the eastern portion
of the lower bays where water clarity is sufficient to support plant survival. Even in these areas, seagrass densities have
recently decreased. Examination of diel dissolved oxygen data collected in the summer indicates progressively larger diel
excursions from lower to upper bays and from open bays to tributary subsystems; however, hypoxic conditions (<2 mg 1−1) were rarely observed in any location. Nitrogen input data (point, surface runoff, groundwater and atmospheric deposition
to surface waters) were assembled for seven regions of the coastal bay system; annual loading rates ranged from 2.4 g N m−2 yr−1 to 39.7 g N m−2 yr−1. Compared with a sampling of loading rates to other coastal systems, those to the upper and lower bays were low while those
to tributaries were moderate to high. Regression analysis indicated significant relationships between annual nitrogen loading
rates and average annual total nitrogen and chlorophyll a concentrations in the water column. Similar analyses also indicated significant relationships between chlorophyll a and the magnitude of diel dissolved oxygen changes in the water column. It is concluded that these simple models, which could
be improved with a well-designed monitoring program, could be used as quantitative management tools to relate habitat conditions
to nutrient loading rates.

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    Biological Conservation 11/2013; 167:57-68. · 4.04 Impact Factor
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    ABSTRACT: A common source of disturbance for coastal aquatic habitats is nutrient enrichment through anthropogenic activities. Although the water column bacterioplankton communities in these environments have been characterized in some cases, changes in α-diversity and/or the abundances of specific taxonomic groups across enriched habitats remain unclear. Here, we investigated the bacterial community changes at three different nutrient-enriched and adjacent undisturbed habitats along the North Coast of Crete: a fish farm, a closed bay within a town with low water renewal rates and a city port, where the level of nutrient enrichment and the trophic status of the habitat were different. Even though changes in α-diversity were different at each site, we observed a common change patern across the sites for five of the most abundant bacterial groups, accounting for most of the community variation: a decrease in the abundance of Pelagibacteraceae and SAR86 and an increase in the abundance of Alteromonadaceae, Rhodobacteraceae and Cryomorphaceae in impacted sites. The abundances of the groups that increased and decreased in impacted sites, were significantly correlated (positively and negatively, respectively) to the total heterotrophic bacteria counts, the concentrations of dissolved organic carbon and/or dissolved nitrogen and chlorophyll-α, indicating that the common change pattern was associated with nutrient enrichment. Our results provide an in-situ indication concerning the association of specific bacterioplankton groups with nutrient enrichment. These groups could be potentially used as indicators for nutrient enrichment if the pattern is confirmed over a broader spatial and temporal scale by future studies.
    Applied and Environmental Microbiology 04/2014; · 3.95 Impact Factor
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    ABSTRACT: We investigated the effects of several environmental factors on eelgrass abundance before, during, and after wide-spread eelgrass diebacks during the unusually hot summer of 2005 in the Chesapeake Bay National Estuarine Re-search Reserve in Virginia. Systematic sampling with fixed transects was used to investigate changes in eelgrass abundance at downriver and upriver regions of the York River Estuary. Concurrently, continuous and discreet mea-surements of water quality were made at fixed stations in each area within the eelgrass beds from 2004 through 2006. Results indicate nearly complete eelgrass vegetative dieback during the July–August period of 2005, in contrast to the more seasonal and typical declines in the summer of 2004. Losses were greatest in the deeper areas of the beds and at the upriver site where light availabilities were lowest. Recovery of eelgrass during 2006 was greater in the downriver area, especially at mid-bed depths. By the fall of 2006, no shoot vegetation remained at the upriver site. In 2005, the frequency and duration of water temperatures exceeding 30C were significantly greater than that of 2004 and 2006. Additionally, the frequencies of low dissolved oxygen excursions of 1–3 mg L 1 during this period were greater in 2005 than 2004 or 2006. These results suggest that eelgrass populations in this estuary are growing near their physiological tolerances. Therefore, the combined effects of short-term exposures to very high summer temper-atures, compounded by reduced oxygen and light conditions, may lead to long-term declines of this species from this system.
    Journal of Coastal Research 07/2008; SI 55:135-147. · 0.76 Impact Factor