Linking Water Quality to Living Resources in a Mid‐atlantic Lagoon System, Usa

Abstract

Abstract. The mid-Atlantic coastal bays are shallow coastal lagoons, separated from the Atlantic Ocean by barrier sand islands with oceanic exchanges restricted to narrow inlets. The relatively poor flushing of these lagoon systems makes them susceptible to eutrophication resulting from anthropogenic nutrient loadings. An intensive water quality and seagrass monitoring program was initiated to track ecological changes in the Maryland and Virginia coastal bays. The purpose of this study was to analyze existing monitoring data to determine status and trends in eutrophication and to determine any associations between water quality and living resources. Analysis of monitoring program data revealed several trends: (1) decadal decreases in nutrient and chlorophyll concentrations, followed by recently increasing trends; (2) decadal increases in seagrass coverage, followed by a recent period of no change; (3) blooms of macroalgae and brown tide microalgae; and (4) exceedance of water quality thresholds: chlorophyll a (15 lg/L), total nitrogen (0.65 mg/L or 46 lmol/L), total phosphorus (0.037 mg/L or 1.2 lmol/L), and dissolved oxygen (5 mg/L) in many areas within the Maryland coastal bays. The water quality thresholds were based on habitat requirements for living resources (seagrass and fish) and used to calculate a water quality index, which was used to compare the bay segments. Strong gradients in water quality were correlated to changes in seagrass coverage between segments. These factors indicate that these coastal bays are in a state of transition, with a suite of metrics indicating degrading conditions. Continued monitoring and intensified management will be required to avert exacerbation of the observed eutrophication trends. Coastal lagoons worldwide are experiencing similar degrading trends due to increasing human pressures, and assessing status and trends relative to biologically relevant thresholds can assist in determining monitoring and management priorities and goals.

Oyster and Macroalgae Bioindicators Detect Elevated δ15N in Maryland’s Coastal Bays

“…Collectively, agricultural fertilizers as well as human and animal wastes have been directly linked to downstream eutrophication (Kennish 2002;Kiddon et al 2003;Bricker et al 2008;Wazniak et al 2007). Long-term water quality monitoring reported recent degradation and increases in total nitrogen despite historical improvements and decreases in total nitrogen, signaling a need to better understand the driving forces for trend shifts in this region and identify sources of anthropogenic nitrogen ).…”

“…Long-term water quality monitoring reported recent degradation and increases in total nitrogen despite historical improvements and decreases in total nitrogen, signaling a need to better understand the driving forces for trend shifts in this region and identify sources of anthropogenic nitrogen ). Symptoms of degradation include an approximate doubling of dissolved organic nitrogen, increasing frequency of harmful algal blooms, e.g., brown tide (Glibert et al 2007), and adverse effects on seagrass distribution and density (Harris et al 2005;Wazniak et al 2007). Human population in Maryland's coastal bays watersheds doubled between 1980 and 2000 to~35,000 people and is expected to double again by 2020 (Hager 1996).…”

A Habitat-Based Framework for Communicating Natural Resource Condition

“…A large number of metrics can be measured over small spatial scales for relatively little expense (e.g., biodiversity and water quality), so it is often useful to aggregate these metrics to get a more stable measure of condition (Figure 2). Aggregation can be accomplished by the mathematical combination of multiple metrics, for example, into a water quality index [22,23] or the benthic index of biotic integrity (BIBI) [24]. Metrics providing information at very large spatial scales are often considered individually within an integrated assessment because they are typically more difficult or costly to obtain or represent one number for a large area such as percent impervious surface [25] (Figure 2).…”

“…Relevant scales for integrated assessments of natural resource condition may vary from 100s of meters, for example, within a managed land such as a national park or between subwatersheds, to 1000s of kilometers, for regional or even global-scale comparisons. Different data and approaches have been applied at these different scales [22,32,33]. In consultation with Park management staff, the assessment scales were determined based on potential management questions and interpretation as well as data availability.…”

Phytoplankton Community Structure Based on Photopigment Markers in a Mid-Atlantic U.S. Coastal Lagoon: Significance for Hard-Clam Production

“…Yet the Tuckerton site exhibited the highest chl a, chl a/N, chl a/C, and TSS concentrations (although a low picoplankton biomass) and typically supported the highest clam-shell growth rates in 2013 and second highest in 2012 (Bricelj et al, unpublished data; results of the present study). Therefore, the indices that are traditionally used to classify water quality in the BB-LEH and other estuaries (including reduction of SAV) (e.g., Ren et al, 2017;Wazniak et al, 2007) may not necessarily correspond to those that provide optimum conditions for hard-clam production. Mercenaria mercenaria can grow well in eutrophic coastal lagoon ecosystems such as Great South Bay, New York (Bricelj, Kraeuter, and Flimlin, 2017;Carmichael, Shriver, and Valiela, 2004), and nutrient ratios rather than bulk eutrophication (N loading) that affect algal composition (and salinity) appear to be more important to characterize suitable conditions for hard-clam somatic and reproductive production.…”