Atmospheric deposition is an important source of nitrogen (N) fueling marine productivity, yet its full impact on ocean carbon export remains poorly constrained. Here, we use a biogeochemical model ensemble for the South China Sea to assess this impact. Our model quantifies that the regenerative recycling of atmospherically deposited N significantly amplifies its fertilizing effect, enhancing annual primary production in offshore waters by ∼22% (∼35 g C m-2 yr-1), which is approximately six times the increase predicted by conventional stoichiometric estimates (∼5.9 g C m-2 yr-1). Beyond production, atmospheric N deposition shifts plankton communities toward larger size classes, increasing annual carbon export at a 100 m depth by 28% and enhancing carbon export efficiency (e-ratio) by 4.4% in offshore waters. Sensitivity experiments further show that the export and efficiency changes are highly sensitive to sinking and remineralization rates of detritus: the e-ratio response can range from a 10.6% decrease to a 5.8% increase, depending entirely on variations in the detritus parameters. These findings, based on the South China Sea, highlight the need for targeted observations to constrain detritus properties and demonstrate that accurate modeling of plankton community structure and detritus dynamics is essential for predicting ocean responses to atmospheric deposition and other nutrient perturbations in similar oligotrophic systems.

Coastal stratification is traditionally considered the primary physical driver of hypoxia by suppressing vertical mixing and dissolved oxygen (DO) ventilation. However, this classical paradigm often fails in highly dynamic estuaries. Using a validated hydrodynamic-biogeochemical model, we reconstructed summer hypoxia in the Pearl River Estuary (PRE) to investigate the physical mechanisms controlling hotspots in the western (WHZ) and eastern (EHZ) shelf regions. A DO budget analysis reveals that, despite significantly stronger stratification, WHZ exhibits a vertical diffusive DO flux that is twice that of EHZ, making it the overwhelmingly dominant term in bottom physical DO supply. This paradox is driven by tidal straining: in WHZ, intense negative tidal straining (<-1.5 & times; 10(-4) psu(2) s(-1)) disrupts stratification and enhances DO diffusion during the late flood phase, even under low shear stress (<0.1 Pa). In contrast, weak tidal straining in the EHZ leaves DO diffusion governed almost entirely by bottom shear stress. Furthermore, in the EHZ, mixing requires nearly a full tidal cycle; by contrast, tidal straining-induced bottom mixing in the WHZ efficiently penetrates the entire water column within half a tidal cycle, making bottom DO dynamics in WHZ strongly tied to stratification fluctuations. This study provides a physical mechanism that explains the bias in the traditional stratification-controlled DO pattern, thereby improving our ability to manage hypoxia in highly dynamic coastal systems.

Land use and rainfall are key drivers of dissolved organic matter (DOM) dynamics in rivers, yet their coupling effects on DOM sources in heterogeneous urbanized watersheds remain unclear. Here we combine fluorescence spectroscopy and stable carbon isotopes within end-member mixing analysis (EMMA) framework to trace DOM sources along the Guangzhou reach of the Pearl River under contrasting land use and rainfall conditions. The optimized three-dimensional subregional EMMA model (BIX-HIX-delta 13C-DOC) substantially outperformed twodimensional and whole-watershed alternatives, reducing prediction error by 45-50%. Upstream agricultural areas were dominated by soil-derived, humic-rich DOM, whereas midstream and downstream urbanized reaches showed greater wastewater contributions and microbial characteristics. Rainfall increases DOM loads across all zones but variably alters source composition depending on land use. The strongest coupling effect occurs in the midstream agricultural-urban transition zone, where rainfall enhances the surface soil input but decreases the wastewater contribution. By comparison, downstream reaches show minimal source shifts after rainfall, reflecting buffering by continuous wastewater inputs. This study evaluates land use-rainfall interactions on DOM sources, and provides an optimized subregional EMMA approach for DOM source apportionment in tropical and subtropical urban rivers.

An increase in riverine nutrient loads has generally been recognized as the primary cause of coastal deoxygenation, whereas the role of other riverine factors, especially suspended sediments, has received less attention. This study aims to discern the impacts of anthropogenic alterations in various riverine inputs on the subsurface deoxygenation over the past three decades in a large river-dominated estuary, the Pearl River estuary (PRE). Using a physical–biogeochemical model, we reproduced the observed dissolved oxygen (DO) conditions off the PRE in the historical period (the 1990s, with a high suspended sediment concentration (SSC), high DO, and low nutrients) and the present period (the 2010s, with low SSC, low DO, and high nutrients). In the 2010s, the PRE exhibited more extensive and persistent summer hypoxia, with the low-oxygen area (DO<4mgL-1) expanding by ∼148 % (to ∼2926 km2) and the hypoxia area (DO<3mgL-1) increasing by 192 % (to ∼617 km2). Low-oxygen durations extended to 15–35 d, and three distinct hypoxic centers formed under different controlling factors. Single-factor experiments suggested that the decreased riverine DO content (46 %) alone expanded low-oxygen areas in the upper estuarine regions by 44 %, the decreased SSC (by 60 %) alone caused a 47 % expansion in the lower reaches of the PRE, and the increased nutrients alone (100 % in dissolved inorganic nitrogen and 225 % in phosphate) drove a 31 % expansion. In comparison, the combined nutrient increases and the SSC declines synergistically enhanced primary production and bottom oxygen consumptions (dominated by sediment oxygen uptake), amplifying low-oxygen (104 %) and hypoxic (192 %) area growth in lower estuaries. Our results revealed that, by improving light availability for productivity, SSC declines play a larger role than nutrient increases in exacerbating deoxygenation off the PRE. This synergy complicates hypoxia mitigation efforts focused solely on nutrient controls. Given the widespread global declines in riverine suspended sediments, our findings underscore the importance of incorporating sediment-mediated processes, a relatively overlooked factor, in coastal deoxygenation studies.

In this study, we collected in situ water quality data during the summer months from 1985 to 2021 and surface sediment organic carbon and stable carbon isotope (δ13C) data from 2002 and 2020 in the Pearl River Estuary (PRE), to analyze long-term trends in hypoxia and explore changes in deoxygenation processes and their potential drivers. Our results showed that hypoxic events in the PRE transitioned from episodic in Lingdingyang Bay in the 2000s to periodic in the lower estuary by the late 2010s. During this transition, the dominant deoxygenation processes shifted from being caused by terrestrial and wastewater emissions to eutrophication. Increased wastewater discharge, reduced sediment load, weakened wind mixing and strengthened coastal upwelling are potential factors contributing to the changes in deoxygenation processes and the deterioration of hypoxic conditions. This study provides a scientific basis for formulating policies to mitigate hypoxia in large estuaries deeply affected by human activities.

Estuarine and coastal environments have experienced dissolved oxygen (DO hereafter) depression and hypoxia due to increasingly intensified anthropogenic eutrophication and climate warming. This review compared diverse systems in Chinese coastal waters that experience DO depletion or hypoxia, aiming to identify essential aspects in advancing the abilities in comprehensively understanding DO dynamics across systems that span wide ranges of physical and biogeochemical environments. The coastal DO depression and relevant ecological consequences around the world are generally overviewed. DO depression in specific systems around Chinese coastal waters, ranging from large estuarine-coastal system to small embayment, are selected to synthetically understand the environment, the controlling processes, the evolution of eutrophication level, and the potential environmental changes under warming trend. Stressed ecosystems would be put at higher risks with high confidence due to increased complexity and uncertainty caused by future socioeconomic transformation and climate warming. This review proposes key aspects to advancing the abilities in predicting, managing, and mitigating DO stress for marine ecosystems in Chinese coastal waters, potentially providing a framework to discuss future DO changes in the coastal waters worldwide.

Deoxygenation in estuarine and coastal waters worldwide has been largely attributed to the increasing anthropogenic nutrient input, whereas the contribution by long-term (decadal) changes in physical forcing is less investigated. This study aims to disentangle the impacts of three-decade changes in summer river nutrient concentration and physical forcing on the deoxygenation off a large eutrophic estuary, the Pearl River Estuary (PRE) in China. Using a coupled physical-biogeochemical model, we reproduce the observed summer oxygen conditions under the historical (the 1990s) and present (the 2020s) status of river nutrient concentration, freshwater discharge, and wind forcing. We show that the bottom hypoxic (dissolved oxygen < 2 mg/L) area off the PRE in the 2020s has increased by 73 % relative to the 1990s. The expansion is a result of the increased bottom water oxygen consumption outweighing the enhanced vertical oxygen supply, with the former driven by the sharp increase in inorganic nitrogen and phosphorus concentrations (160 %) and the latter caused by the decadal decline in both freshwater discharge (38 %) and wind speed (12.5 %) in summer. Model experiments suggest that if the observed changes in physical forcing had not occurred, the dramatic increase in anthropogenic nutrient concentrations from the 1990s to 2020s could have led to a much greater expansion of hypoxic area (249 %). On the contrary, the decadal decrease in summer freshwater discharge alone (while keeping the nutrient loading the same as in the 1990s) almost eliminates hypoxia off the PRE by weakening water column stratification and limiting the offshore spread of nutrients and organic matter, whereas the declined wind speed increases the hypoxic area by 247 % mainly through enhancing water column stability. Our results reveal that long-term changes in physical forcing are confounding the effects of anthropogenic nutrient input on deoxygenation, underlining the need to consider regional forcing changes in nutrient management to meet water quality goals.

Tides have significant effects on material and energy transports over the continental shelf. A mooring system located in the shelf region of the northeastern South China Sea observed strong and weak mean currents during the spring and neap tides in summer, respectively. The mechanism leading to this difference is investigated by using a three-dimensional circulation model. We find that the impact of tides (TI) on currents exhibited as current components opposing wind-driven circulation play an important role. The TI current components are stronger than the tidal residual currents in summer when vertical stratification enhances the tidal rectification. Tides can affect pressure gradient by modifying sea surface height on the shelf, while in shallow and shelf break regions, the non-linear advection and vertical diffusion become significant in momentum equations attributable to the interactions of tidal currents, bottom topography and water column stratification. Consequently, the along-shelf volume transport is reduced by about 21.6% due to the TI current components and only by about 6.1% due to the tidal residual currents. This study highlights the importance of both tidal mixing and tidal rectification in regulating shelf circulation in the northeastern South China Sea.

Water hypoxia and metal pollution are commonly co-existed in urbanized estuaries. This study focuses on the effect of an extended dissolved oxygen (DO) full-life dynamics (86 days) on metal behavior across the sediment-water interface through laboratory microcosms from two typical zones in Pearl River Estuary. Combining our time-series results of concentrations and fluxes, it showed that Co, Ni, and Zn consistently presented a release-precipitation-release trajectory with an oxic-hypoxic-anoxic-reoxic transition, characterized with highly variable behavior in the hypoxic-anoxic hotmoments. In parallel, changing DO dynamics significantly activated a repartitioning process of Co, Ni, and Zn among several species and elevated their risk in sediments, promoting the formation of more labile species in the 0–10 mm hotspots, where metals sensitively responded. Over DO transition, metal cycling was tightly co-related with Fe, Mn, and S elements. It was found that Mn was dominated in low oxygen-hypoxic period, but switched to S and Fe in anoxic stage, limiting sustained metal liberation to overlying water. Enlarging this experiment to practice, released Zn fluxes from sediments in hypoxic summer could contribute about ~2.0 % to their stocks in water column, while increase to 20 % (1 m bottom water) in highly-stratified zones. This study has certain significance in understanding the long-term metal behavior and fate in estuarine regions, even lakes and reservoirs.

Study region: Dongjiang River Network (DJRN), a complex urbanized river network in the Pearl River Basin, China. Study focus: Low-oxygen conditions have been expanding in urbanized river systems, whereas a clear and quantitative understanding on the deoxygenation processes is still lacking. This study utilized a well-validated physical-biogeochemical model to investigate the oxygen dynamics combined with river ecosystem metabolisms over an annual cycle and explicitly quantify the contribution of major oxygen-depleting substances from different sources to low-oxygen conditions. New hydrological insight for the region: Our results showed significant spatiotemporal variations in low-oxygen extents and oxygen source-sink patterns in the DJRN, where the underlying control mechanisms varied across stream order due to the intricate geographic and hydrological regime shifts in conjunction with diverse pollution stressors. Ascribed to the seasonal variations in anthropogenic pollution and water temperature, the entire DJRN shifted to a completely heterotrophic system with severe oxygen deficits during the late summer and early autumn. Scenario simulations indicated that in line with the substantial wastewater control in the DJRN region, local pollutant loads played a trivial role in the low-oxygen generation, which instead was primarily fueled by organic matter from transboundary delivery and in-situ primary production. Our findings underscored the necessity of co-regional collaborative management on pollutant emissions and the importance of eutrophication mitigation for the sake of oxygen recovery in the urbanized river network.

The influence of overlying hydrodynamics on the exchange behaviour and fluxes of heavy metals at the sediment-water interface (SWI) is poorly understood. In the study, metals exchange behaviour and exchange rate at the SWI under resuspended and undisturbed scenario were investigated The results showed that dissolved Cr, Cu, Zn, and Pb concentrations increased rapidly to attain maximum values between 0.3 and 0.5 N center dot m(-2) after the sediment resuspended. Following the quick release, metals concentrations gradually decreased and remained at relatively low levels, especially for Cu and Zn. Meanwhile, Cu, Zn, and Pb had higher potential remobilization potential in the undisturbed case. Calculating with the hydrodynamics in the Modaomen, the metals efflux under the resuspension scenario could reach 0.55 to 4130.83 mg center dot m(-2)center dot yr(-1), which were 1-3 orders of magnitudes higher than the undisturbed case. Whether or not resuspension events occurred, estuarine sediments were source of heavy metals, especially in the weakly mixed zone.

Shiziyang Bay, located in the upstream of the Pearl River Estuary, has frequently suffered from hypoxia since 2000, which has persisted in recent years despite effective controls on anthropogenic pollutant loads. To explore the underlying causes, changes in dissolved oxygen (DO), nutrients, chemical oxygen demand (COD), and chlorophyll a (Chl a) along the bay in response to altered pollutant inputs were investigated using observations collected in summers of 2015-2019 and historical data during 2000-2008. In addition, DO sources and sinks were calculated based on data from August 2020 and laboratory incubations for water column respiration (WCR) and sediment oxygen uptake, and were compared with their equivalents in August 2008 to elucidate changes in primary processes controlling hypoxia. The results showed that ammonia has decreased significantly with pollutant control, while other parameters responded in different trends, especially for Chl a (with a substantial increase over time). The intensified eutrophication contributed to high COD levels, leading to a strong WCR (as dominant oxygen depletion) close to that in the 2000s and thereby maintaining low-oxygen conditions despite reduced effluent discharges. The shifted primary oxygen-consuming substances from allochthonous inputs to in-situ phytoplankton production were also evidenced by significant correlation between oxygen consumption rate and Chl a in recent data. Simultaneously, the enhanced algal blooms could also modulate oxygen supply, resulting in higher photosynthetic oxygen production and lower air-sea reaeration compared with the past. Furthermore, the impact of major environmental changes on exacerbated eutrophication was explored and it was speculated that notable declined sediment loads would be important by improving light conditions to promote phytoplankton proliferation in the bay. Collectively, substantial control on eutrophication as well as tracking DO source-to-sink processes is of great importance to mitigate hypoxia in Shiziyang bay.

The summertime low-oxygen conditions in the Pearl River Estuary (PRE) have experienced a significant spatial expansion associated with notable deoxygenation in recent decades. Nevertheless, there is still a lack of quantitative data on the long-term trends and interannual variabilities in oxygen conditions in the PRE as well as on the driving factors. Therefore, the long-term deoxygenation in a subregion of the PRE (the coastal waters off Hong Kong) was comprehensively investigated in this study using monthly observations during 1994–2018. To evaluate the changes in scope and intensity of oxygen conditions, an indicator (defined as the low-oxygen index, LOI) that integrates several metrics related to low-oxygen conditions was introduced as the result of a principal component analysis (PCA). Moreover, primary physical and biogeochemical factors controlling the interannual variabilities and long-term trends in oxygen conditions were discerned, and their relative contributions were quantified by multiple regression analysis. Results showed that the regression models explained over 60 % of the interannual variations in LOI. Both the wind speeds and concentrations of dissolved inorganic nitrogen (DIN) played a significant role in determining the interannual variations (by 39 % and 49 %, respectively) and long-term trends (by 39 % and 56 %, respectively) in LOI. Due to the increasing nutrient loads and alterations in physical conditions (e.g., the long-term decreasing trend in wind speeds), coastal eutrophication was exaggerated and massive marine-sourced organic matter was subsequently produced, thereby resulting in an expansion of intensified low-oxygen conditions. The deteriorating eutrophication has also driven a shift in the dominant source of organic matter from terrestrial inputs to in situ primary production, which has probably led to an earlier onset of hypoxia in summer. In summary, the Hong Kong waters have undergone considerable deterioration of low-oxygen conditions driven by substantial changes in anthropogenic eutrophication and external physical factors.

Abstract. The summertime low-oxygen conditions in the Pearl River Estuary (PRE) have experienced a significant expansion in spatial extent associated with notable deoxygenation in recent decades. Nevertheless, there is still a lack of quantitative understanding of the long-term trends and interannual variabilities in oxygen conditions in the PRE as well as the driving factors, which was comprehensively investigated in this study using monthly observations in the eastern PRE during 1994–2018. To evaluate the changes in scope and intensity of oxygen conditions, an indicator (defined as the Low-oxygen Index, LOI) that integrates several metrics related to low-oxygen conditions was introduced through the principal component analysis (PCA). Moreover, primary physical and biogeochemical factors controlling the interannual variabilities and long-term trends in oxygen conditions were discerned, and their relative contributions were quantified by the multiple regression analysis. Results showed that the regression models explained over 60 % of the interannual variations in LOI. Both the wind speeds and concentrations of dissolved inorganic nitrogen (DIN) played a significant role in determining the interannual variations (by 39 % and 49 %, respectively) and long-term trends (by 39 % and 56 %, respectively) in LOI. Due to the increasing nutrient loads and alterations in physical conditions (e.g. the long-term decreasing trend in wind speeds), coastal eutrophication was exaggerated and massive marine-sourced organic matter was subsequently produced, thereby resulting in an expansion of intensified low-oxygen conditions. It has also driven a shift in the dominant source of organic matter from terrestrial inputs to in situ primary production, which has probably led to an earlier onset of hypoxia in summer. In summary, the eastern PRE has undergone considerable deterioration of low-oxygen conditions in the context of substantial changes in anthropogenic eutrophication and external physical factors.

合流制管网溢流(combined sewer overflows,CSOs)是造成我国城镇地表水环境污染的重要原因.文中以广州市东山湖及其相关排水管网为研究对象,通过构建东山湖水动力、水质模型,模拟分析现状条件下CSOs对东山湖水质的影响,以及DN3000支隧建成后对东山湖水质的改善效果.结果表明,DN3000支隧对东山湖CSOs污染防治起到明显作用,该工程建成后,可以保证在典型暴雨时期,东山湖全水域内CODCr、TN、TP均可满足《地表水环境质量标准》(GB 3838—2002)IV类标准.

本文利用2018年1月盐水上溯期间在磨刀门区域所获得的现场调查资料,分析该区域的重金属污染现状及空间分布特征,探究重金属的迁移转化特点以及盐度等环境因素对重金属分配结果的影响.基于水体盐度及层化水平将研究区域分为淡水区、混合区及咸水区.结果表明,颗粒态与溶解态重金属含量在淡水区与咸水区之间存在显著差异,颗粒态重金属含量均呈现出由陆向海方向随盐度增加而降低的趋势,各元素的空间变异程度依次为Cd＞Cr＞Zn＞Pb＞Cu＞As＞Ni＞Co;溶解态Pb、Cr、As、Co浓度沿向海方向呈逐渐升高趋势,而Cd、Cu、Ni、Zn浓度则呈现"低—高—低"的变化特征,各元素的空间变异程度依次为Zn＞Cr＞Cd＞Pb＞Cu＞Co＞As＞Ni.重金属的固液分配系数沿向海方向呈逐渐下降趋势,主成分分析结果表明,盐度和悬浮物浓度是影响磨刀门河口重金属分配的主要环境因素.

Our understanding of eutrophication-induced acidification in estuaries and coastal oceans is complicated by the seasonally and spatially changing interactions between physical and biochemical drivers. By combining the conservative mixing method and a physical-biogeochemical model, we present the seasonal and spatial dynamical analysis of eutrophication-induced acidification in the Pearl River Estuary in the northern South China Sea. In summer, the widespread eutrophication-induced acidification is regulated by two distinct physical drivers, which are the strengthened stratification in the hypoxia zone and the high turbidity in the Lingdingyang Bay. In the hypoxia zone, eutrophication-induced acidification is controlled by the combined effect of benthic remineralization and stratification, while it is dominantly regulated by local biochemical processes (nitrification and respiration) of the whole water column in other regions of the estuary. In winter with the enhanced vertical mixing, the eutrophication-induced acidification is still active in the Lingdingyang Bay, and its strength has largely decreased compared with summer condition. While for the hypoxia zone, the eutrophication-induced acidification peaks in summer and disappears in winter. Plain Language Summary Eutrophication in estuaries has accelerated the ocean acidification, which induced a negative impact on marine ecosystem. In the estuary, physical and biochemical processes lead to difficulties in understanding and evaluating the impact of eutrophication-induced acidification. High-resolution and coupled oceanographic models can reproduce the biogeochemical cycles in the marine system and present an integrated framework to understand ocean acidification. We revealed two distinct types of eutrophication-induced acidification in the estuary by using an oceanographic model. The model results show that these two types of eutrophication-induced acidification are regulated by different physical processes that are water stratification and turbidity, which result in their unique seasonal evolution patterns.

Located in the northern South China Sea, the Pearl River Estuary (PRE) is one of the most important estuaries in China and is surrounded by several megacities. Hypoxia mainly occurs in the bottom waters of the PRE during summer and is more prominent near the Humen outlet and the subestuary outside Modaomen and Jitimen. A well-validated three-dimensional (3-D) coupled physical-biogeochemical model was used to explore the changes in dissolved oxygen (DO) dynamics and hypoxic conditions in the PRE over an intra-annual cycle and elucidate the processes controlling the generation, development, and dissipation of hypoxia. In summer, oxygen consumption due to the high-intensity sediment oxygen demand (SOD) intensified by large inputs of riverine particulate organic carbon (POC) exceeded the DO supplemented by vertical diffusion (largely inhibited by strong fresh water–induced stratification), thus leading to a significant decrease in DO in the bottom waters; in other seasons, these DO source and sink terms were nearly balanced so that the bottom DO concentrations were maintained at higher levels. Moreover, the lag analysis shows that there is an approximately 2-month lag between riverine POC and SOD. By comparison, the low-oxygen area near Humen has a controlling mechanism distinct from that of the subestuary outside Modaomen and Jitimen. Specifically, the timely and sufficient oxygen supplement brought by vertical diffusion can replenish the bottom DO consumed by SOD in this region, and the formation and development of low-oxygen conditions (DO ≤ 4 mg L−1) is mainly affected by riverine low-oxygen inflows. In summary, our study clarified that the terrestrial organic pollutant input and low-oxygen water from the upper reaches have an important impact on the DO in different areas of the PRE, especially the low-oxygen area near Humen, which is controlled by the water quality of the upper reaches. This conclusion is of great significance for regional environmental management.

Many estuaries have undergone severe saltwater intrusion in addition to simultaneously experiencing serious heavy metal pollution. To explore the effect of water density stratification associated with saltwater intrusion on the behaviour of heavy metals (Cr, Co, Ni, Cu, Zn, As, Pb, and Cd) in water and sediments, a field survey was conducted in a typical estuary (Modaomen). The content, distribution, and mobility of heavy metals were investigated, as well as the influence of environmental factors on their future. The results showed that Modaomen estuary was characterised by a notable variation in salinity along the estuary, presenting total freshwater upstream, high salinity stratification water in the mouth, and saltwater offshore. Dissolved metals presented a prominent gradient vertically, with 1.2-2.1 times higher in bottom water than in surface water and the highest contents in the highly-stratified bottom water. Elevated salinity and restricted mixing induced by water stratification were likely the causes of this outcome. The distribution of heavy metals in sediments was greatly governed by grain size, Fe/Mn (hydr)oxides, total organic carbon, salinity, and dissolved oxygen. Comprehensive evaluation, combined with total contents and chemical fractions of heavy metals, indicated that internal release from sediments contributed a considerable part to the higher levels of heavy metals in bottom water, particularly for Zn and Pb, which was fully consistent with their status in water body, and elevated salinity and lack of oxygen were likely the primary driving factors. During the phase-partition processes between bottom water and sediments, partitioning coefficients were markedly lower in the highly stratified zone, implying that saltwater intrusion facilitated the mobility and repartitioning processes of metals. Because of increased levels and toxicity of heavy metals in water and extended residence time during saltwater intrusion, the potential damage to the estuarine ecosystem should receive more attention.