Oxygen and Nutrient Exchanges at the Sediment-Water Interface: a Global Synthesis and Critique of Estuarine and Coastal Data

Estuarine and coastal marine sediment-water fluxes are considered to be important ecological features, but a global-scale assessment has yet to be developed. Goals of this work were to assemble a global-scale database of net sediment-water flux measurements, examine measurement techniques, characterize the geographic distribution and magnitude of sediment fluxes, explore the data for controls on sediment flux magnitude, and assess the importance of sediment fluxes in ecosystem-level metabolism and primary production. We examined 480 peer-reviewed sources and found sediment flux data for 167 estuarine and coastal systems. Most measurements were made in North America, Europe, and Australia. Fluxes varied widely among systems, some by several orders of magnitude. Inter-annual variability within sites was less than an order of magnitude but time series flux data to evaluate this were rare. However, limited time series data exhibited large and rapid responses to decreased external nutrient loading rates, climate change effects (possible temperature effects), and variability in trophic conditions. Comparative analyses indicated organic matter supply to sediments set the upper limits of flux magnitude, with other factors playing secondary roles. Two metrics were developed to assess ecosystem-level importance of sediment-water fluxes. Sediments represented 30% or more of depth-integrated rates of aerobic system respiration at depths of <10 m. An annual phytoplankton production data set was used to estimate N and P demand; sediments supplied an average of 15–32% of N and 17–100% of P demand and, in some cases, was as large or larger than external nutrient inputs. The percent of demand supplied by sediments was highest in temperate latitudes and lower in high and tropical latitudes.     

Chesapeake Bay Plume Morphology and the Effects on Nutrient Dynamics and Primary Productivity in the Coastal Zone

To determine the effects of the Chesapeake Bay outflow plume on the coastal ocean, nutrient concentrations and climatology were evaluated in conjunction with nitrogen (N) and carbon (C) uptake rates during a 3-year field study. Sixteen cruises included all seasons and captured high- and low-flow freshwater input scenarios. Event-scale disturbances in freshwater flow and wind speed and direction strongly influenced the location and type of plume present and thus the biological uptake of N and C. As expected, volumetric primary productivity rates did not always correlate with chlorophyll a concentrations, suggesting that high freshwater flow does not translate into high productivity in the coastal zone; rather, high productivity was observed during periods where recycling processes may have dominated. Results suggest that timing of meteorological events, with respect to upwelling or downwelling favorable conditions, plays a crucial role in determining the impact of the estuarine plume on the coastal ocean.     

Benthic Respiration and Inorganic Nutrient Fluxes in the Estuarine Region of Patos Lagoon (Brazil)

In situ benthic flux chamber experiments were performed during late austral spring and early summer of 1996 at eleven nearshore locations in the southern Patos Lagoon, Brazil. The Patos Lagoon is the largest lagoonal system in South America and is a very important nursery ground for local fin fish and shell fish fisheries. These are the first benthic flux measurements made in Patos Lagoon and they suggest that remineralizationwithin the sediments may dominate the recycling of organic matter and nutrients in thelagoon. Measured oxygen benthic fluxes (45–160 mmol m^-2 d^-1) are sufficientto remineralize reported mean water column carbon fixation while phosphate and fixednitrogen benthic fluxes (-0.4–2 and -1.1–4.2 mmol m^-2 d^-1, respectively)are sufficient to supply 100% and 25% of the required water column nutrient demand,respectively. Although of limited areal and temporal coverage, these initial studiesdemonstrate that sediments play a major role in the metabolism and nutrient cyclingwithin the Patos Lagoon Estuary and that future studies of lagoonal biogeochemistrymust consider exchange with the bottom.     

Enhanced Benthic Nutrient Flux During Monsoon Periods in a Coastal Lake Formed by Tideland Reclamation

Sediment and water quality were investigated in an artificial coastal lake (Saemangeum Lake, Korea) that was formed by constructing a 33-km long sea-dyke offshore from the mouths of two adjacent rivers, which discharge into the Yellow Sea. Sediment showed drastic increases in fine fraction (silt and clay) after the dyke construction. TN, TP, and OC contents in the sediment showed the similar spatial variation to that of fine fraction. A mixing model indicated benthic fluxes of nutrients such as PO₄, NH₄, and SiO₂, which were considerably elevated during the summer monsoon season. It is revealed that this phenomenon was associated with the development of strong salinity stratification, elevated water temperature, and increased groundwater discharge. However, a change in the sedimentation environment due to dyke construction is suggested as the primary reason for the enhanced benthic fluxes.     

Direct and Indirect Interactions Between Lower Estuarine Mangrove and Saltmarsh Habitats and a Commercially Important Penaeid Shrimp

Vegetated habitats in estuaries may provide a structural refuge and food supply in the same place, but benefits are also derived where a productive food source and suitable habitat are adjacent to each other. Quantifying these relationships is fundamental to understanding the structural and functional characteristics of estuarine ecosystems and for informing management actions. Effective juvenile habitat (habitat that contributes greater-than-average numbers of recruits to the adult population), recruitment patterns and trophic relationships were studied for Eastern King Prawn (Penaeus plebejus) in the lower Clarence River estuary, New South Wales, between 2014 and 2016. Effective juvenile habitat was identified in both the north arm and main river channel of the estuary, and these areas also supported a higher abundance of juvenile prawns. There was minimal recruitment to the southern channels of the estuary, possibly due to reduced connectivity with the incoming tide arising from a rock wall. Trophic relationships in parts of the lower estuary were evaluated using stable isotopes, and saltmarsh grass (Sporobolus virginicus) was the dominant primary producer supporting juvenile Eastern King Prawn productivity across the area. Mangroves were of minimal importance, and seagrass cover was minimal in the area studied. The patterns observed indicate that nursery function of different areas within the lower estuary is a product of connectivity, recruitment and nutrition derived from primary productivity of vascular plants. Habitats within the lower Clarence River estuary have seen substantial degradation over decadal time scales, and the implications of our findings for targeting future habitat repair are discussed.     

Contrasting Bacterial Dynamics in Subtropical Estuarine and Coastal Waters

Seasonal succession and composition of both attached and free-living bacterial communities were studied in subtropical estuarine and coastal waters with contrasting hydrographic conditions. A higher abundance of attached bacteria was recovered in the estuarine waters containing high concentrations of dissolved organic carbon (DOC) resulting from the freshwater discharge in the adjacent Pearl River, and Proteobacteria, including ??-, ??-, and ??-groups, predominated the attached community at both stations. Free-living bacterial communities at both stations showed higher diversity and lower seasonality than their attached counterparts, and ??-Proteobacteria accounted for the highest proportion at both stations. Redundancy analysis (RDA) demonstrated that, in addition to the obvious temperature effects, DOC and microphytoplankton (>20???m Chl a) drive the temporal variation of attached bacteria at the estuarine and coastal stations, respectively. On the other hand, picophytoplankton (<2???m Chl a) and dissolved oxygen concentration explained most of the free-living bacterial community succession at the estuarine station, while those at the coastal station were associated with micro- and picoplankton (Chl a fractions of <2 and >20???m). These findings suggest that temperature and bottom?Cup effects play a more important role for the spatial?Ctemporal variations of both attached and free-living bacterial communities in the subtropical estuarine and coastal waters.     

Global Nitrogen Cycle: Pre-Anthropocene Mass and Isotope Fluxes and the Effects of Human Perturbations

We present a nitrogen cycle model for pre-industrial times based on an extensive literature database. The model consists of 18 reservoirs in the domains of the atmosphere, land, and ocean. The biotic reservoirs on land and in the ocean (N-fixing plants, non-N-fixing plants, and marine biota) interact with atmospheric N₂ and dissolved inorganic nitrogen (DIN, consisting of N₂, NO₃ ^?, and NH₄ ⁺) in the ocean and soil waters. Marine DIN is taken up by marine biota and transformed from ocean particulate organic matter to dissolved organic nitrogen and the ocean sediment. The atmosphere, the largest nitrogen reservoir, supplies N₂ to the system by N fixation, deposition, and dissolution, and these input fluxes are balanced by denitrification and volatilization back to the atmosphere. The land and ocean domains are linked by river transport, which carries both dissolved and particulate nitrogen to the oceanic coastal zone. The isotope–mass balances of the N reservoirs are calculated from the isotopic composition of the reservoirs and the fractionation factors accompanying the fluxes between the reservoirs based on reported values from different natural conditions. The model sensitivity was tested for different biouptake rates and was run with various human perturbations, including fertilization, nitrous oxide emissions, population-related sewage disposal, land-use changes, and temperature-dependent rate kinetics. The new N mass–isotope cycle model provides the basis for assessment of the impact of artificial fertilization between 1700 and 2050. The perturbation experiments in this study suggest that land-use change is the key factor altering the N mass cycle since industrialization.     

Indirect Hurricane Effects on Resource Availability and Microbial Communities in a Subtropical Wetland-Estuary Transition Zone

Three sequential hurricanes made landfall over the South Florida peninsula in August and September 2004. The storm systems passed north of the Everglades wetlands and northeastern Florida Bay, but indirect storm effects associated with changes in freshwater discharge during an otherwise drought year occurred across the wetland–estuary transition area. To assess the impacts of the 2004 hurricane series on hydrology, nutrients, and microbial communities in the Everglades wetlands to Florida Bay transition area, results are presented in the context of a seasonal cycle without hurricane activity (2003). Tropical activity in 2004 increased rainfall over South Florida and the study area, thereby temporarily relieving drought conditions. Not so much actual rainfall levels at the study site but more so water management practices in preparation of the hurricane threats, which include draining of an extensive freshwater canal system into the coastal ocean to mitigate inland flooding, rapidly reversed hypersalinity in the wetlands-estuary study area. Although annual discharge was comparable in both years, freshwater discharge in 2004 occurred predominantly during the late wet season, whereas discharge was distributed evenly over the 2003 wet season. Total organic carbon (TOC), ammonium ( \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} ), and soluble reactive phosphorus (SRP) concentrations increased during the hurricane series to concentrations two to five times higher than long-term median concentrations in eastern Florida Bay. Spatiotemporal patterns in these resource enrichments suggest that TOC and SRP originated from the Everglades mangrove ecotone, while \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} originated from the bay. Phytoplankton biomass in the bay increased significantly during storm-related freshwater discharge, but declined at the same time in the wetland mangrove ecotone from bloom conditions during the preceding drought. In the bay, these changes were associated with increased nanophytoplankton and decreased picophytoplankton biomass. Heterotrophic bacterial production increased in response to freshwater discharge, whereas bacterial abundance decreased. Hydrochemical and microbial changes were short-lived, and the wetland–bay transition area reverted to more typical oligotrophic conditions within 3 months after the hurricanes. These results suggest that changes in freshwater discharge after drought conditions and during the hurricane series forced the productivity and P-enriched characteristics of the wetland’s mangrove ecotone, although only briefly, to the south into Florida Bay.     

河口海岸GIS时空过程可视化表达

河口海岸带中一些随时间变化的三维海洋现象(如涡漩、锋面、水团等)的时空建模与可视化表达是海洋地理信息系统(MGIS)发展的一大难题。基于流体建模与可视化AVIZO Green技术,针对海洋连续场中的三维海洋现象,提出了基于特征的时空三域动态识别技术,设计并实现了面向主题应用的时空四维GIS可视化框架,能够有效表达三维海洋现象。以长江口海岸带涡漩、冲淡水、羽状锋和盐跃层为例进行三维动态可视模拟,直观再现了object-like型和field-like型海洋现象的时空演绎过程,为海洋现象仿真研究,尤其是多维、动态、边界模糊的复杂海洋现象的有效表达提供了一种新思路和方法。     

Nutrient Fluxes from Sediments in the San Francisco Bay Delta

In September 2011 and March 2012, benthic nutrient fluxes were measured in the San Francisco Bay Delta, across a gradient from above the confluence of the Sacramento and San Joaquin Rivers to Suisun Bay. Dark and illuminated core incubation techniques were used to measure rates of denitrification, nutrient fluxes (phosphate, ammonium, nitrate), and oxygen fluxes. While benthic nutrient fluxes have been assessed at several sites in northern San Francisco Bay, such data across a Delta–Bay transect have not previously been determined. Average September rates of DIN (nitrate, nitrite, ammonium) flux were net positive across all sites, while March DIN flux indicated net uptake of DIN at some sites. Denitrification rates based on the N₂/Ar ratio approach were between 0.6 and 1.0 mmol m^?2 day^?1, similar to other mesotrophic estuarine sediments. Coupled nitrification–denitrification was the dominant denitrification pathway in September, with higher overlying water nitrate concentrations in March resulting in denitrification driven by nitrate flux into the sediments. Estimated benthic microalgal productivity was variable and surprisingly high in Delta sediments and may represent a major source of labile carbon to this ecosystem. Variable N/P stoichiometry was observed in these sediments, with deviations from Redfield driven by processes such as denitrification, variable light/dark uptake of nutrients by microalgae, and adsorption of soluble reactive phosphorus.     

基于遥感和GIS的上海市滩涂湿地资源近期变化分析

利用多期Landsat-5 TM影像,结合植被分带信息、地物波谱特征和实地调查数据,提取上海地区滩涂湿地分布及其覆盖信息;在ArcGIS软件支持下,综合多期遥感影像解译结果和相应时段的水下地形信息,对上海市滩涂湿地空间分布及其变化进行分析。结果表明,近15年来上海市滩涂围垦量在不断增加;尽管滩涂湿地仍在继续淤涨,但淤涨速度明显减缓,且慢于围垦速度,这导致中高潮滩涂面积不断减少。     

Evaluating Adaptive Processes for Conservation and Management of Estuarine and Coastal Resources

This special feature: Genetic Structure and Adaptation in Coastal Ecosystems emphasizes the importance of research focused on population genetic structure and evolutionary change for understanding estuarine and coastal communities. Many studies have examined the effect of environmental gradients on community-level patterns in estuarine habitats; however, relatively little is known about the role of genetically based adaptation (the heritable response to these environmental gradients) in these organisms. This special feature presents 11 studies that use a variety of approaches including ecophysiology, ecological genetics, molecular markers, and patterns of gene expression occurring within these populations. These studies provide examples of the role of genetic diversity and adaptation across a diversity of estuarine and coastal environments, and highlight the temporal and spatial scales at which adaptation impinges upon management. This collection of papers is especially timely, given the increasing importance of understanding and predicting the response to global climate change in order to effectively manage these communities.     

The Contribution of Groundwater Discharge to Nutrient Exports from a Coastal Catchment: Post-Flood Seepage Increases Estuarine N/P Ratios

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 NO _x , 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, NO _x , 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.     

中国海岸带环境地质编图研究

中国海岸带环境地质图(1:400万)综合反映了我国海岸带区域性地质环境基本特征、主要环境地质问题与地质灾害、近岸海域水文条件以及人类工程-经济活动强度.本文反映了编制中国海岸带环境地质图的基本原则、图面范围、主要内容、表示方法与环境地质分区.     

The Invasive Species Challenge in Estuarine and Coastal Environments: Marrying Management and Science

Despite the widely acknowledged threat posed by invasive species in coastal estuaries, there are substantial gaps at the intersection of science and policy that are impeding invasive species management. In the face of pressing management needs in coastal and estuarine environments, we advocate that introduced species should receive the kind of management effort dedicated, for example, to reducing pollution. We support our argument with some examples of economic costs of estuarine and coastal introduced species and a summary of recent evidence for the ecological costs. We highlight some of the issues that either thwart or facilitate the successful marriage between science and management of introduced species, including the regulatory framework for management. We use the available information on coastal eradication programs, including case histories of the programs for Caulerpa taxifolia and Spartina alterniflora (and hybrids) in the western USA, to indicate the feasibility of managing introduced species and to help point out how management and science can improve the outcome. We close with a research agenda that focuses primarily on science that will really assist with invasive species management and reflects our own experience and the opinions of managers directly involved with this issue.     

Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA

We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7–0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (?4.9 to 49 mmol m^?2 day^?1) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m^?2 day^?1. In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH₄) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l^?1 at Calusa in the eastern bay to a mean of 0.6 μmol l^?1 at Rabbit Key for the period of study. However, average NH₄ fluxes by site and date (?240 to 110 μmol m^?2 h^?1) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15–25 μmol l^?1), were greater than mean NH₄ concentrations, and the range of day and night DON fluxes (?920 to 1,300 μmol m^?2 h^?1), averaged by site and date, was greater than the range of mean NH₄ fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from ?590 to 860 μmol m^?2 h^?1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021–0.075 μmol l^?1); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04–0.15 μmol l^?1) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1–12 μmol g DW^?1) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (?5.2 to 52 μmol m^?2 h^?1), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (?8.7 to 7.4 μmol m^?2 h^?1), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means?=?0.66–7.4 μmol g DW^?1). Significant correlations of nutrient fluxes with parameters related to seagrass abundance suggest that the seagrass community may play a major role in nutrient recycling. Integrated means of net daily fluxes over the area of Florida Bay, though highly variable, suggest that seagrass communities might be a source of DOP and NH₄ to Florida Bay and might remove small amounts of FRP and potentially large amounts of DON from the waters of the bay.     

全国海岸带地质环境综合数据集

全国海岸带地质环境综合数据集为海岸带综合地质调查工程的数据成果,按照陆海统筹的总体思路设计,重点实现海陆调查专业学科全覆盖,技术方法手段全覆盖。数据内容主要包括野外综合调查、野外综合施工、野外动态监测、样品测试4大类,共计数据表130个,数据177 592条。其中野外综合调查类包含9个数据表,9 006条数据;野外综合施工类包含68个数据表,89 551条数据;野外动态监测类包含28个数据表,12 305条数据;样品测试类包含25个数据表,66 730条数据。本数据集为海岸带自然资源统一管理、国土空间规划和用途管制以及生态保护修复等提供高效精准的数据服务。     

Carbon Dioxide Fluxes and Their Environmental Control in a Reclaimed Coastal Wetland in the Yangtze Estuary

Large areas of natural coastal wetlands have suffered severely from human-driven damages or conversions (e.g., land reclamations), but coastal carbon flux responses in reclaimed wetlands are largely unknown. The lack of knowledge of the environmental control mechanisms of carbon fluxes also limits the carbon budget management of reclaimed wetlands. The net ecosystem exchange (NEE) in a coastal wetland at Dongtan of Chongming Island in the Yangtze estuary was monitored throughout 2012 using the eddy covariance technique more than 14 years after this wetland was reclaimed using dykes to stop tidal flooding. The driving biophysical variables of NEE were also examined. The results showed that NEE displayed marked diurnal and seasonal variations. The monthly mean NEE showed that this ecosystem functioned as a CO₂ sink during 9 months of the year, with a maximum value in September (?101.2 g C m^?2) and a minimum value in November (?8.2 g C m^?2). The annual CO₂ balance of the reclaimed coastal wetland was ?558.4 g C m^?2 year^?1. The ratio of ecosystem respiration (ER) to gross primary production (GPP) was 0.57, which suggests that 57 % of the organic carbon assimilated by wetland plants was consumed by plant respiration and soil heterotrophic respiration. Stepwise multiple linear regressions suggested that temperature and photosynthetically active radiation (PAR) were the two dominant micrometeorological variables driving seasonal variations in NEE, while soil moisture (M _s) and soil salinity (PS_s) played minor roles. For the entire year, PAR and daytime NEE were significantly correlated, as well as temperature and nighttime NEE. These nonlinear relationships varied seasonally: the maximum ecosystem photosynthetic rate (A _max), apparent quantum yield (?), and Q ₁₀ reached their peak values during summer (17.09 μmol CO₂?m^?2 s^?1), autumn (0.13 μmol CO₂?μmol^?1 photon), and spring (2.16), respectively. Exceptionally high M _s or PS_s values indirectly restricted ecosystem CO₂ fixation capacity by reducing the PAR sensitivity of the NEE. The leaf area index (LAI) and live aboveground biomass (AGB_L) were significantly correlated with NEE during the growing season. Although the annual net CO₂ fixation rate of the coastal reclaimed wetland was distinctly lower than the unreclaimed coastal wetland in the same region, it was quite high relative to many inland freshwater wetlands and estuarine/coastal wetlands located at latitudes higher than this site. Thus, it is concluded that although the net CO₂ fixation capacity of the coastal wetland was reduced by land reclamation, it can still perform as an important CO₂ sink.     

Estimation of Groundwater and Nutrient Fluxes to the Neuse River Estuary, North Carolina

A study was conducted between April 2004 and September 2005 to estimate groundwater and nutrient discharge to the Neuse River estuary in North Carolina. The largest groundwater fluxes were observed to occur generally within 20 m of the shoreline. Groundwater flux estimates based on seepage meter measurements ranged from 2.86?×?10⁸ to 4.33?×?10⁸ m³ annually and are comparable to estimates made using radon, a simple water-budget method, and estimates derived by using Darcy’s Law and previously published general aquifer characteristics of the area. The lower groundwater flux estimate (equal to about 9 m³ s^?1), which assumed the narrowest groundwater discharge zone (20 m) of three zone widths selected for an area west of New Bern, North Carolina, most closely agrees with groundwater flux estimates made using radon (3–9 m³ s^?1) and Darcy’s Law (about 9 m³ s^?1). A groundwater flux of 9 m³ s^?1 is about 40% of the surface-water flow to the Neuse River estuary between Streets Ferry and the mouth of the estuary and about 7% of the surface-water inflow from areas upstream. Estimates of annual nitrogen (333 tonnes) and phosphorus (66 tonnes) fluxes from groundwater to the estuary, based on this analysis, are less than 6% of the nitrogen and phosphorus inputs derived from all sources (excluding oceanic inputs), and approximately 8% of the nitrogen and 17% of the phosphorus annual inputs from surface-water inflow to the Neuse River estuary assuming a mean annual precipitation of 1.27 m. We provide quantitative evidence, derived from three methods, that the contribution of water and nutrients from groundwater discharge to the Neuse River estuary is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment sources of nutrients. Locally high groundwater discharges do occur, however, and could help explain the occurrence of localized phytoplankton blooms, submerged aquatic vegetation, or fish kills.