Use of historical isoscapes to develop an estuarine nutrient baseline

Coastal eutrophication is a prevalent threat to the healthy functioning of ecosystems globally. While degraded water quality can be detected by monitoring oxygen, nutrient concentrations, and algal abundance, establishing regulatory guidelines is complicated by a lack of baseline data (e.g., pre-Anthropocene). We use historical carbon and nitrogen isoscapes over ~300 years from sediment cores to reconstruct spatial and temporal changes in nutrient dynamics for a central California estuary, Elkhorn Slough, where development and agriculture dramatically enhanced nutrient inputs over the past century. We found strong contrasts between current sediment stable isotopes and those from the recent past, demonstrating shifts exceeding those in previously studied eutrophic estuaries and substantial increases in nutrient inputs. Comparisons of contemporary with historical isoscapes also revealed that nitrogen sources shifted from a historical marine-terrestrial gradient with higher δ15N near the inlet to amplified denitrification at the head and mouth of the modern estuary driven by increased N inputs. Geospatial analysis of historical data suggests that an increase in fertilizer application – rather than population growth or increases in the extent of cultivated land – is chiefly responsible for increasing nutrient loads during the 20th century. This study demonstrates the ability of isotopic and stoichiometric maps to provide important perspectives on long-term shifts and spatial patterns of nutrients that can be used to improve management of nutrient pollution

Nitrogen control through decentralized wastewater treatment: Process performance and alternative management strategies

Decentralized or onsite wastewater treatment (OWT) systems have long been implicated in being a major source of N inputs to surface and ground waters and numerous regulatory bodies have promulgated strict total N (TN) effluent standards in N-sensitive areas. These standards, however, most of which have effluent limitations of \u3c10. mg/L TN, were generally developed without data on treatment performance and attainable compliance levels of operating OWTs designed to remove N. This paper reviews OWT technologies that rely on preanoxic or postanoxic denitrification, or simultaneous nitrification-denitrification, and frequently include compact, mechanized components. TN effluent data from 20 OWTs in 3 long-term N removal demonstration projects in Florida, Oregon, and New Zealand are analyzed and compared with the performance of 15 centralized N removal treatment plants from the US and Canada. A reliability and stability analysis shows that only one of the 20 OWTs approaches the reliability and stability of centralized plants, and can comply with a \u3c10. mg/L TN effluent standard with a 99% probability; all of the remaining 19 OWTs have a \u3c50% probability of compliance. The lower reliability of OWTs, many of which are energy-intensive, scaled-down models of centralized plants, is due to the inherent variability of decentralized wastewater characteristics and the challenges of operationally controlling N removal processes at the level of residences. However, the small footprint (required land area) of these compact designs offers important opportunities for retrofitting OWTs on small lots, in shoreline developments where land is at a premium and where communities wish to foster and sustain compact, village developments that reflect smart growth strategies. Other approaches to decentralized N management emphasizing passive, robust, ecologically engineered designs are reviewed and include natural wastewater treatment systems such as single pass sand filters with denitrifying bioreactors, which performed better than any other OWT technology; shallow trenches and drip irrigation for denitrification or plant N uptake in the carbon-rich root zone; denitrification beds/layers installed down gradient from effluent plumes; and the consideration of watershed N sinks in estimating the risks of N loading to receiving waters. These alternative approaches require further research and development, but can offer alternatives or additional treatment to mechanized OWTs. More comparative studies of long-term operation of OWTs under field conditions in other parts of the world are needed to further quantify performance capabilities. © 2010 Elsevier B.V

A marked gradient in δ\u3csup\u3e13\u3c/sup\u3eC values of clams Mercenaria mercenaria across a marine embayment may reflect variations in ecosystem metabolism

Although stable isotopes of organic carbon (δ13C) are typically used as indicators of terrestrial, intertidal, andoffshore organic carbon sources to coastal ecosystems, there is evidence that δ13C values are also sensitive to in situecosystem metabolism. To investigate this phenomenon, we examined δ13C values of filter-feeding hard clams Mercenaria mercenaria from 13 locations in Greenwich Bay, a sub-estuary of Narragansett Bay, Rhode Island (USA). The δ13C values ofthe clams showed a marked linear gradient of 2‰ over the 4 kmlength of Greenwich Bay (-19 to -17‰), from lower δ13C values in the inner bay to higher values at the mouth, where Greenwich Bay joins Narragansett Bay proper (R2 = 0.94, p \u3c 0.0001). This is in contrast to previous work that has shown that δ13C values of clams in Narragansett Bay proper (over 40 km long) are homogenous (mean × SD, -16.8 × 0.6 ‰, n = 247). Mean daily pH, temperature, and salinitydata from 2 fixed monitoring stations were used to estimate aqueous CO2(CO2(aq)) concentrations in the surroundingwater. CO2(aq) concentrations were higher in inner Greenwich Bay than immediately outside of the bay, suggesting that the dissolved inorganic carbon sources supporting phytoplankton production are quite different across the bay. The outer Greenwich Bay clams appear to feed on Narragansett Bay phytoplankton with higher δ13C values that are grown in a higher pH, more bicarbonate-rich environment. In contrast, the inner Greenwich Bay clams may feedon phytoplankton grown in lower pH water with a greater availabilityof CO2(aq). The lower δ13C of CO2(aq) relative to HCO3 - is reflected in the phytoplankton and in the clams that feed on them. Our work suggests that δ13C values may be sensitive to changes in inorganic C in estuarine systems, which may confound attempts to use stable isotopesto identify organic carbon sources. © Inter-Research 2010

Anthropogenic enhancement of Egypt\u27s Mediterranean fishery

The highly productive coastal Mediterranean fishery off the Nile River delta collapsed after the completion of the Aswan High Dam in 1965. But the fishery has been recovering dramatically since the mid-1980s, coincident with large increases in fertilizer application and sewage discharge in Egypt. We use stable isotopes of nitrogen (δ15N) to demonstrate that 60%–100% of the current fishery production may be from primary production stimulated by nutrients from fertilizer and sewage runoff. Although the establishment of the dam put Egypt in an ideal position to observe the impact of rapid increases in nutrient loading on coastal productivity in an extremely oligotrophic sea, the Egyptian situation is not unique. Such anthropogenically enhanced fisheries also may occur along the northern rim of the Mediterranean and offshore of some rapidly developing tropical countries, where nutrient concentrations in the coastal waters were previously very low

Fresh Water Inflow and Oyster Productivity in Apalachicola Bay, FL (USA)

Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds have long been thought to contribute to the support of an unusually productive and commercially important oyster fishery. Links between the river and productivity have been shown to lie in salinity-induced reductions in oyster predators and oyster disease as well as organic supplements from an extensive floodplain. Several studies have also indicated that nitrogen (N) and phosphorous (P) carried by the river are important in fertilization of bay primary production. While there is concern that upstream water withdrawals may impact the fishery, the importance of riverine N to oyster diets remains unclear. We measured N and carbon (C) stable isotopes (δ15N, δ13C) in macroalgae, surface-water nitrate, and surface sediments, which showed a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope values throughout Apalachicola Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine inflows. © 2011 Coastal and Estuarine Research Federation (outside the USA)

The Role of Snowmelt and Spring Rainfall in Inorganic Nutrient Fluxes from a Large Temperate Watershed, the Androscoggin River Basin (Maine and New Hampshire)

The importance of snowmelt and spring rainfall to water and nutrient exports from macro-scale watersheds (\u3e1000 km2) is not well established. Data collected from the Androscoggin River watershed (Maine and New Hampshire) between February 1999 and March 2002 show that the 90-day spring melt period accounted for 39–57% of total annual discharge and is likely driven both by snowpack melting and spring rainfall. While large loads of dissolved inorganic nitrogen (DIN) are delivered to the watershed from snowmelt and rain (from 1.16× 106 to 1.61× 106 kg N over the study years), only one third of this N load is exported from the basin during the snowmelt period (0.40× 106–0.48 × 106 kg N). Despite reduced residence time and temperature limitations on biological N retention, there is a poor mass balance between DIN input to the watershed and the nitrogen exported from mouth of the river. Inferences from a geochemical hydrograph separation suggests that approximately 51–63% of the water leaving the mouth of the Androscoggin river is from these ‘new’ water sources (rain and snowmelt) while 37–49% is from DIN depleted soil and groundwater. Mixing of water from different sources, as well as nutrient retention by dams in the upper watershed, may account for the large discrepancy between DIN inputs and exports from this watershed

On the Response of pH to Inorganic Nutrient Enrichment in Well-Mixed Coastal Marine Waters

Abstract Recent concerns about declining pH in the surface ocean in response to anthropogenic increases of carbon dioxide (CO 2 ) in the atmosphere have raised the question of how this declining baseline of oceanic pH might interact with the much larger diel and seasonal variations of pH in coastal marine ecosystems. Nutrient enrichment, which can amplify both production and respiration, has the potential to reduce or exacerbate the impacts of ocean acidification in coastal waters. Here, we present results from a multi-year experiment in which replicate phytoplankton-based mesocosms with a 5-m deep well-mixed water column (salinity = 27-31) and intact benthic community were exposed to a gradient in daily inorganic nitrogen (N), phosphorous (P), and silica (Si) addition. We show that the response of water column pH to nutrient enrichment was the greatest during the autotrophic winterspring period, and there was no significant decline in pH across treatments during the heterotrophic summer-fall period. We believe that the differences in response lie in the seasonal cycles of production and respiration, where spring production peaks are large and discrete, and respiration is more temperature-driven but occurs diffusely throughout the year. The observed basification associated with enhanced nutrient inputs may have consequences for phytoplankton community structure, some species of submersed aquatic vegetation, cycling of Si, and perhaps other ecological processes

Tidal Flushing Rather Than Non-Point Source Nitrogen Pollution Drives Nutrient Dynamics in A Putatively Eutrophic Estuary

The effects of nonpoint source nutrients on estuaries can be difficult to pinpoint, with researchers often using indicator species, monitoring, and models to detect influence and change. Here, we made stable isotope measurements of nitrogen and carbon in sediment, water column particulates, primary producers, and consumers at 35 stations in the reportedly eutrophic Barnegat Bay (New Jersey) to assess N sources and processing pathways. Combined with water quality and hydrological data, our C and N isoscapes revealed four distinct geographic zones with diverging isotopic baselines, indicating variable nutrient sources and processing pathways. Overall, the carbon stable isotopes (δ13C) reflected the terrestrial-marine gradient with the most depleted values in the urban and poorly flushed north of the estuary to the most enriched values in the salt marsh-dominated south. In contrast, the nitrogen stable isotope values (δ15N) were most enriched near the oceanic inlets and were consistent with offshore δ15N values in particulate organic matter. Several biogeochemical processes likely alter δ15N, but the relatively lower δ15N values associated with the most urbanized area indicate that anthropogenic runoff is not a dominant N source to this area. Our findings stand in contrast to previous studies of similar estuaries, as δ15N signatures of biota in this system are inversely correlated to population density and nutrient concentrations. Further, our analyses of archival plant (Spartina sp., Phragmites australis) and shell (Geukensia demissa, Ilyanassa obsoleta) samples collected between 1880 and 2020 indicated that δ15N values have decreased over time, particularly in the consumers. Overall, we find that water quality issues appear to be most acute in the poorly flushed parts of Barnegat Bay and emphasize the important role that oceanic exchange plays in water quality and associated estuarine food webs in the lagoon

Recent nitrogen storage and accumulation rates in mangrove soils exceed historic rates in the urbanized San Juan Bay Estuary (Puerto Rico, United States)

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wigand, C., Oczkowski, A. J., Branoff, B. L., Eagle, M., Hanson, A., Martin, R. M., Balogh, S., Miller, K. M., Huertas, E., Loffredo, J., & Watson, E. B. Recent nitrogen storage and accumulation rates in mangrove soils exceed historic rates in the urbanized San Juan Bay Estuary (Puerto Rico, United States). Frontiers in Forests and Global Change, 4, (2021): 765896, https://doi.org/10.3389/ffgc.2021.765896.Tropical mangrove forests have been described as “coastal kidneys,” promoting sediment deposition and filtering contaminants, including excess nutrients. Coastal areas throughout the world are experiencing increased human activities, resulting in altered geomorphology, hydrology, and nutrient inputs. To effectively manage and sustain coastal mangroves, it is important to understand nitrogen (N) storage and accumulation in systems where human activities are causing rapid changes in N inputs and cycling. We examined N storage and accumulation rates in recent (1970 – 2016) and historic (1930 – 1970) decades in the context of urbanization in the San Juan Bay Estuary (SJBE, Puerto Rico), using mangrove soil cores that were radiometrically dated. Local anthropogenic stressors can alter N storage rates in peri-urban mangrove systems either directly by increasing N soil fertility or indirectly by altering hydrology (e.g., dredging, filling, and canalization). Nitrogen accumulation rates were greater in recent decades than historic decades at Piñones Forest and Martin Peña East. Martin Peña East was characterized by high urbanization, and Piñones, by the least urbanization in the SJBE. The mangrove forest at Martin Peña East fringed a poorly drained canal and often received raw sewage inputs, with N accumulation rates ranging from 17.7 to 37.9 g m–2 y–1 in recent decades. The Piñones Forest was isolated and had low flushing, possibly exacerbated by river damming, with N accumulation rates ranging from 18.6 to 24.2 g m–2 y–1 in recent decades. Nearly all (96.3%) of the estuary-wide mangrove N (9.4 Mg ha–1) was stored in the soils with 7.1 Mg ha–1 sequestered during 1970–2017 (0–18 cm) and 2.3 Mg ha–1 during 1930–1970 (19–28 cm). Estuary-wide mangrove soil N accumulation rates were over twice as great in recent decades (0.18 ± 0.002 Mg ha–1y–1) than historically (0.08 ± 0.001 Mg ha–1y–1). Nitrogen accumulation rates in SJBE mangrove soils in recent times were twofold larger than the rate of human-consumed food N that is exported as wastewater (0.08 Mg ha–1 y–1), suggesting the potential for mangroves to sequester human-derived N. Conservation and effective management of mangrove forests and their surrounding watersheds in the Anthropocene are important for maintaining water quality in coastal communities throughout tropical regions.Some funding was provided by the United States Geological Coastal and Marine Hazards and Resources Program