Chesapeake Bay's water quality condition has been recovering: Insights from a multimetric indicator assessment of thirty years of tidal monitoring data

Zhang, Qian; Murphy, Rebecca R.; Tian, Richard; Forsyth, Melinda K.; Trentacoste, Emily M.; Keisman, Jennifer; Tango, Peter J.

doi:10.1016/j.scitotenv.2018.05.025

Cited by 66 publications

(46 citation statements)

References 39 publications

(49 reference statements)

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“…First, Kemp omitted data from years that diverged from average conditions, while 2016 was a dry year. Less discharge, combined with reductions in nitrogen inputs and chlorophyll (Zhang et al, 2018) and nitrogen removal by SAV beds that have grown in area by 50 km 2 since 1998 (Gurbisz and Kemp, 2014;Orth et al, 2017), likely resulted in reduced eutrophication and consequently, lower productivity in the mesohaline and polyhaline regions. So, our net export flux estimates are compatible with the previous organic carbon budget.…”

Section: Discussionmentioning

confidence: 99%

Chesapeake Bay Inorganic Carbon: Spatial Distribution and Seasonal Variability

Brodeur

Chen

et al. 2019

Front. Mar. Sci.

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Few estuaries have inorganic carbon datasets with sufficient spatial and temporal coverage for identifying acidification baselines, seasonal cycles and trends. The Chesapeake Bay, though one of the most well-studied estuarine systems in the world, is no exception. To date, there have only been observational studies of inorganic carbon distribution and flux in lower bay sub-estuaries. Here, we address this knowledge gap with results from the first complete observational study of inorganic carbon along the main stem. Dissolved inorganic carbon (DIC) and total alkalinity (TA) increased from surface to bottom and north to south over the course of 2016, mainly driven by seasonal changes in river discharge, mixing, and biological carbon dioxide (CO 2 ) removal at the surface and release in the subsurface. Upper, mid-and lower bay DIC and TA ranged from 1000-1300, 1300-1800, and 1700-1900 µmol kg −1 , respectively. The pH range was large, with maximum values of 8.5 at the surface and minimums as low as 7.1 in bottom water in the upper and mid-bay. Seasonally, the upper bay was the most variable for DIC and TA, but pH was more variable in the mid-bay. Our results reveal that low pH is a continuing concern, despite reductions in nutrient inputs. There was active internal recycling of DIC and TA, with a large inorganic carbon removal in the upper bay and at salinities < 5 most months, and a large addition in the mid-salinities. In spring and summer, waters with salinities between 10 and 15 were a large source of DIC, likely due to remineralization of organic matter and dissolution of CaCO 3 . We estimate that the estuarine export flux of DIC and TA in 2016 was 40.3 ± 8.2 × 10 9 mol yr −1 and 47.1 ± 8.6 × 10 9 mol yr −1 . The estuary was likely a large sink of DIC, and possibly a weak source of TA. These results support the argument that the Chesapeake Bay may be an exception to the long-standing assumption that estuaries are heterotrophic. Furthermore, they underline the importance of large estuarine systems for mitigating acidification in coastal ecosystems, since riverine chemistry is substantially modified within the estuary.

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Section: Discussionmentioning

confidence: 99%

Chesapeake Bay Inorganic Carbon: Spatial Distribution and Seasonal Variability

Brodeur

Chen

et al. 2019

Front. Mar. Sci.

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“…Testa et al (2018) reported a decline in NH 4 and an increase in NO 2+3 concentrations in channel bottom waters during late summer as dissolved oxygen concentrations have increased, suggesting a vicious biogeochemical cycle may be breaking (Kemp et al, 2005). Zhang et al (2018) demonstrated progressive improvement in a multimetric index of water quality attainment that integrates dissolved oxygen, water clarity, submersed vascular vegetation and chlorophyll a. This began in the late 1990s following wastewater treatment plant upgrades and reductions in atmospheric deposition of nitrogen.…”

Section: Chesapeake Baymentioning

confidence: 99%

Barriers and Bridges in Abating Coastal Eutrophication

Boesch

2019

Front. Mar. Sci.

127

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Over the past 30 years concerted campaigns have been undertaken to reverse nutrient-driven eutrophication in coastal waters in Europe, North America, Asia, and Australia. Typically, eutrophication abatement has proven a more recalcitrant challenge than anticipated, with ecosystem improvements only recently beginning to emerge or falling short of goals. Reduction in nutrient loads has come mainly from advanced treatment of wastewaters and has lagged targets set for diffuse agricultural sources. Synthesis of the major campaigns-varying in terms of physical settings, ecosystem characteristics, nutrient sources, socio-economic drivers, and governance-identified barriers inhibiting eutrophication abatement and potential bridges to overcome them. Actionable science can be advanced by: application of the well-established and emerging knowledge and experience around the globe, client-responsive strategic research, and timely and conclusive adjudication of scientific controversies. More accountable governance requires: enduring engagement of high-level officials of the responsible governments; effective communication of the causes, risks and benefits to the public and stakeholders; quantitative and accountable allocation of responsibility for nutrient load reductions; and binding requirements, as opposed to simply voluntary actions. Effective reduction in nutrient loads requires: reduction strategies for both nitrogen and phosphorus; inclusion of actions that reduce atmospheric emissions of nitrogen in addition to direct inputs to waterways; efficacious regulations; public subsidies based on performance; limitations on biofuel production that increases nutrient loads; and enhancing the sinks and losses for legacy nutrients retained in soils and groundwater. Outcomes must be measured and strategies appropriately adjusted through: sustained monitoring of essential indicators and processes, the use of multiple models, truly adaptive management, and cautious interventions within the coastal ecosystem. The changing climate must be taken into account by reassessing achievable future conditions and seeking alternatives for mitigating and adapting to climate change that also reduce nutrient loads.

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“…Excess nutrients can cause hypoxic zones, algal blooms, and fish kills (Boesch et al 2001, Burgin and Hamilton 2007, Perez 2015. Though many parts of the Bay are showing water quality improvement, as of 2016, 58% of Bay tidal waters did not meet standards for dissolved oxygen, chlorophyll a, and water clarity, key indicators of good water quality (Zhang et al 2018). In 2017, the U.S. Geological Survey found increasing N and P loads at several monitoring stations along major tributaries that drain into the Bay (Moyer and Blomquist 2018).…”

Section: Study Sitementioning

confidence: 99%

Saltwater intrusion affects nutrient concentrations in soil porewater and surface waters of coastal habitats

Weissman

Tully

2020

Ecosphere

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Coastal ecosystems are undergoing major biogeochemical shifts due to climate change and sea level rise. At the same time, agricultural fertilizer applications are increasing coastal nutrient inputs. In this study, we examine the potential impact of saltwater intrusion (SWI) on nitrogen (N) and phosphorus (P) concentrations in soil porewater and surface water of different habitats within the Chesapeake Bay estuary. Study sites are located along Maryland's Lower Eastern Shore and were monitored over three summers from 2016 to 2018. These sites encompass various habitats on the land–sea interface, consisting of healthy forests, intruded forests, abandoned fields, intruded fields, agricultural ditches, tidal creeks, and tidal salt marshes. Intruded fields were being actively farmed at the time of the study. Soil porewater and surface water grab samples were collected from the habitats and analyzed for electrical conductivity, pH, dissolved organic P (DOP), dissolved inorganic P in the form of soluble reactive P (SRP), dissolved inorganic N as ammonium‐N (NH4‐N), and total dissolved iron (TDFe). Electrical conductivity was greatest in the marshes (16.58 mS/cm averaged across all years) and did not significantly differ among intruded forests, intruded fields, and agricultural ditches. As a legacy of heavy fertilizer use, DOP concentrations exceeded 0.45 mg P/L in all habitats. Concentrations of inorganic N and P differed significantly by habitat. Concentrations of NH4‐N were significantly higher in salt marsh soil porewater than in any other habitat measured. Overall, SRP concentrations were the highest in the soil porewater of intruded fields and marshes and in the surface water of agricultural ditches (0.30, 0.29, and 0.33 mg P/L averaged across all years, respectively). These concentrations greatly exceeded recommended U.S. Environmental Protection Agency nutrient pollution thresholds for the region. In its oxidized state, dissolved iron can bind to SRP and prevent it from becoming bioavailable. However, TDFe concentrations in the ditches, tidal creeks, and marshes were too low to adequately buffer against SRP loss to downstream areas. As SWI moves salts inland and increases hydrologic connectivity across coastal landscapes, it is important to consider the mechanisms through which nutrients may be released from coastal soils and their potential to impact downstream water quality.

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Chesapeake Bay's water quality condition has been recovering: Insights from a multimetric indicator assessment of thirty years of tidal monitoring data

Cited by 66 publications

References 39 publications

Chesapeake Bay Inorganic Carbon: Spatial Distribution and Seasonal Variability

Chesapeake Bay Inorganic Carbon: Spatial Distribution and Seasonal Variability

Barriers and Bridges in Abating Coastal Eutrophication

Saltwater intrusion affects nutrient concentrations in soil porewater and surface waters of coastal habitats

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