大辽河口营养物基准推导方法

河口富营养化与流域氮、磷营养物的输入直接相关，制定河口营养物基准，可用于控制河口及其近岸海域富营养化，为环境管理的科学决策提供依据。大辽河是渤海最大的入海河流之一，河口污染较为严重；本文采用频数分布法、非参数分析法和实验室模拟压力响应关系法探讨大辽河口及近岸海域营养物基准的推导，最终得到大辽河口总氮（TN）、总磷（TP）及叶绿素a（Chl-a）推荐基准值分别为1.008 mg/L，0.067 mg/L和1.175 mg/m³，以期为大辽河口及其近岸海域富营养化评估和营养物标准制定提供科学依据。     

Effects of agricultural and urban land cover on New Zealand’s estuarine water quality

ABSTRACT

National-scale analyses of land cover effects on water quality can aid in directing environmental policy. We compiled a coastal water quality database for New Zealand comprising 320 estuarine and coastal sites with records between 2013 and 2018. Previous literature had shown strong effects of agricultural and urban land cover on the quality of New Zealand’s rivers, so we examined their effects on estuaries, while controlling for marine dilution and freshwater flushing. Sites with greater freshwater influence had higher nutrient and faecal indicator bacteria concentrations, and turbidity, indicating that open coast and estuarine water quality is reduced predominantly via flows from the land. Nitrate, ammonium, total and dissolved reactive phosphorus, and water column chlorophyll-a concentrations were greater in estuaries with higher urban land cover and total phosphorus concentrations were greater with higher agricultural land cover. There was a marginally significant increase in turbidity as agricultural land cover increased. This is the first national-scale compilation and analysis of New Zealand coastal water quality data, and the first national analysis of land cover effects on water quality in New Zealand estuaries.     

Decoupling of nutrient and grazer impacts on a benthic estuarine diatom assemblage

Strong interactions between top-down (consumptive) and bottom-up (resource supply) trophic factors occur in many aquatic communities, but these forces can act independently in some microphytobenthic communities. Within benthic estuarine diatom assemblages, the dynamics of these interactions and how they vary with abiotic environmental conditions are not well understood. We conducted a field experiment at two sites with varying habitat characteristics to investigate the interactive effects of grazers and nutrients on benthic estuarine diatoms. We crossed snail (Cerithidea californica) and nutrient (nitrogen and phosphorus) addition treatments in enclosures on a restored tidal sandflat and a reference tidal mudflat in Mugu Lagoon, southern California. We repeated the study in summer 2000 and spring 2001 to assess temporal variation in the interactions. Snails caused a large decrease in diatom relative abundance and biomass (estimated as surface area); nutrients increased diatom abundance but did not alter diatom biomass. Snails and nutrients both reduced average diatom length, although the nutrient effect was weaker and temporally variable, occurring in the reference mudflat in the spring. There were few interactions between snail and nutrient addition treatments, suggesting that links between top-down and bottom-up forces on the diatom community were weak. There were no consistent differences in diatom assemblage characteristics between the two study sites, despite marked differences in sediment grain size and other abiotic characteristics between the sites. The strong diatom response to herbivores and weaker responses to enrichment differed from the previous studies where cyanobacteria increased in response to nutrient enrichment, further dissolving the “black box” perception of microphytobenthic communities.     

Ecosystem shift resulting from loss of eelgrass and other submerged aquatic vegetation in two estuarine lagoons, Lake Nakaumi and Lake Shinji, Japan

Zostera marina L. was intensively harvested until the early 1950s in Lake Nakaumi, a eutrophic estuarine lagoon. We have estimated the amount of nitrogen (N) and phosphorus (P) removed from the lagoon through Z. marina harvesting. Lake Nakaumi lies in Tottori and Shimane prefectures, and the annual harvest of Z. marina in the late 1940s in Tottori was recorded as at least 56,250 t wet weight. The nutrient content of 56,250 t of Z. marina was calculated to be 61.9 t of N and 12.9 t of P, which is equivalent to 5.3% and 11%, respectively, of present annual nutrient loads to the lake. The nutrients formerly used by Z. marina were likely used by phytoplankton after the Z. marina started to decline in the mid-1950s at Lake Nakaumi. This shift in the chief primary producer, from benthic macrophytes to phytoplankton, caused a subsequent shift in secondary producers. Benthic fish and crustacean populations decreased and the non-commercial filter-feeding bivalve, Musculus senhausia, increased in Lake Nakaumi after the decline of seagrass beds. This affected the local economy, inducing not only eutrophication but also the collapse of local fisheries. On the other hand, at adjacent Lake Shinji, loss of submerged aquatic vegetation induced an increase of the commercial filter-feeding bivalve, Corbicula japonica, which doubled the fishery yield in the lake.     

近海生态系统的人为营养盐输入及其控制对策浅析

人为活动每年新增大量的活性氮、磷，导致全球氮、磷循环失衡，新增活性氮、磷主要来源于合成氮肥的生产和施用、畜肥的施用、具固氮能力的农作物如豆科植物等的大规模种植，以及化石燃料燃烧产生的氮氧化物等，而农作物生产与畜禽养殖是改变全球氮、磷循环的主要原因。随着生活污水排放量和化肥施用量的激增，大量氮、磷进入近海，导致营养盐污染和富营养化，这已成为全球性的海洋生态环境问题，通过河流径流和大气沉降进入近海生态环境中的新增氮和磷一半以上与人为活动有关。本文以波罗的海和东海为例，分析了发达国家和发展中国家近海的富营养化问题，研究表明从源头缓解富营养化的对策应同时聚焦氮与磷负荷的削减，具体措施包括降低农业生产活动中化肥的土壤渗漏、合理施肥、种植多年生植物和种植休耕季覆被作物等。     

Comparison of Monsoonal change of water quality parameters between 1983 and 2008 in a tropical estuary in Northeastern India: role of phytoplankton and community metabolism

Ongoing climate change and anthropogenic activities are introducing stressors that affect the structure and function of coastal ecosystems. This paper focuses on the fluvial fluxes and estuarine transport of nutrients from a tropical river (Mahanadi River) in Northeastern India and compares select nutrient and water quality parameters between 1983 and 2008. This estuary acts as a perennial source of CO₂ with a net annual flux to the atmosphere of about 135 tons. The non‐conservative fluxes showed a net annual removal of 650 and 140 tons of phosphorus and nitrogen from the water column, respectively. Negative biogeochemical feedbacks that decreased the availability of N and P in 2008 relative to 1983 levels indicate major changes in biogeochemical responses towards fluvial fluxes of nutrient.     

Typhoon-induced precipitation impact on nutrient and suspended matter dynamics of a tropical estuary affected by human activities in Hainan,China

Typhoons regularly hit the coasts along the northern South China Sea during summer monsoon. However, little is known on the effects of typhoon-related heavy precipitation on estuarine dynamics and coastal ecosystems. We analyzed physico-chemical characteristics, and concentrations and composition of dissolved and suspended matter in the Wenchang/Wenjiao Estuary (WWE) on the tropical island of Hainan, China, prior to and after typhoon Kammuri in August 2008. Before the typhoon, the estuary displayed vertical and horizontal gradients. High nutrient inputs from agriculture and widespread aquaculture were to a large extent converted into biomass inside the estuarine lagoon resulting in low export of nutrients to coastal waters and a mainly autochthonous origin of total suspended matter (TSM). Heavy typhoon-associated precipitation increased river runoff, which moved the location of the estuarine salinity gradient seaward. It resulted in an export of dissolved and particulate matter to coastal waters one day after the typhoon. Dissolved nutrients increased by up to an order of magnitude and TSM increased approximately twofold compared to pre-typhoon values. Lower δ¹³C_org and δ¹⁵N and elevated C/N ratios of TSM together with lower chlorophyll a (chl a) concentrations indicated an increased contribution of terrestrial material originating from typhoon-induced soil erosion. Local uptake of excess nutrients inside the lagoon was inhibited because of reduced water transparency and the lack of phytoplankton, which had been washed out by the initial freshwater pulse. Two weeks after the typhoon, TSM concentration and composition had almost returned to pre-typhoon conditions. However, physico-chemical properties and nutrients were still different from pre-typhoon conditions indicating that the estuarine system had not fully recovered. Unusually high chl a concentrations in the coastal zone indicated a phytoplankton bloom resulting from the typhoon-induced nutrient export. The typhoon-induced flushing of the WWE resulted in hyposalinity, reduced water transparency, siltation, as well as temporary eutrophication of coastal waters. These are physiological stressors, which are known to impair the performance of adjacent seagrass meadows and coral reefs. The predicted increase in typhoon frequency and intensity will lead to a frequently recurring exposure of coastal ecosystems to these threats, particularly in the South China Sea region where aquaculture is widespread and tropical cyclone frequency is at a maximum.     

Bottom-up control of phytoplankton growth in spring blooms in Central Yellow Sea,China

The source and significance of three nutrients – nitrogen, phosphorous and silicon – were investigated by a modified dilution method performed on seawater samples from the Central Yellow Sea (CYS), in spring blooming period of 2007. This modified dilution method accounted for the phytoplankton growth rate, microzooplankton grazing mortality rate, the internal and external nutrient pools, as well as nutrients supplied through remineralization by microzooplankton grazing. The results indicate that phytoplankton growth during the bloom is mostly contributed by internal nutrient pools (K_I=0.062–1.730). The external nutrient pools (K_E=<0–0.362) are also of importance for phytoplankton growth during the bloom at some sampling sites. Furthermore, the contribution of the recycled-nutrient pool by remineralization (K_R=<0–0.751) is significant when microzooplankton grazing rate was higher than 0.5 d⁻¹ during the spring phytoplankton blooms in the Central Yellow Sea. Compared with internal phosphorus, internal nitrogen and silicon contribute more to the phytoplankton production at most sampling stations.     

Three dimensional water quality modeling of a shallow subtropical estuary

Knowledge of estuarine hydrodynamics and water quality comes mostly from studies of large estuarine systems. The processes affecting algae, nutrients, and dissolved oxygen (DO) in small and shallow subtropical estuaries are relatively less studied. This paper documents the development, calibration, and verification of a three dimensional (3D) water quality model for the St. Lucie Estuary (SLE), a small and shallow estuary located on the east coast of south Florida. The water quality model is calibrated and verified using two years of measured data. Statistical analyses indicate that the model is capable of reproducing key water quality characteristics of the estuary within an acceptable range of accuracy. The calibrated model is further applied to study hydrodynamic and eutrophication processes in the estuary. Modeling results reveal that high algae concentrations in the estuary are likely caused by excessive nutrient and algae supplies in freshwater inflows. While algal blooms may lead to reduced DO concentrations near the bottom of the waterbody, this study indicates that stratification and circulation induced by freshwater inflows may also contribute significantly to bottom water hypoxia in the estuary. It is also found that high freshwater inflows from one of the tributaries can change the circulation pattern and nutrient loading, thereby impacting water quality conditions of the entire estuary. Restoration plans for the SLE ecosystem need to consider both a reduction of nutrient loading and regulation of the freshwater discharge pattern.     

Ammonium and phosphorus flux through the microplankton community in Agulhas Bank waters

The size-related activities of important heterotrophs and autotrophs were compared at the surface and at the subsurface chlorophyll maximum (Chl_max) in Agulhas Bank waters. The netplankton fraction was dominated by Nitzschia spp. and ciliates, small (diameter c. 3μm) microflagellates being the most abundant nanoplankton group. Uptake ratios of ammonium to phosphate for the total microplankton community were different at the two depths. With reference to the Redfield ratio, it appears that at least 48 per cent of the nitrogen ration at the Chl_max was regenerated even though nitrate was in ample supply. These assimilation ratios also suggest a very large contribution from recycled nitrogen other than ammonium in surface waters. It is unlikely that phosphorus would ever become limiting, except perhaps at the primary production maximum. Microplankton uptake and regeneration of both ammonium and phosphorus were approximately in balance, indicating that variations in assimilation ratios were the result of heterotrophic excretory activity. The size-fractionation studies show that picoplankton were on average the single most important size class in nutrient assimilation. The netplankton size class was, in terms of regeneration, often the most active in the microplankton community especially within the Chl_max. Heterotrophic microflagellates and picoplankton supplied the bulk of ammonium and phosphorus at the surface. The importance of a particular size class to either ammonium or phosphorus uptake/excretion was quantified as a relative assimilation/regeneration index. These calculations demonstrate size-related differences in the relative importance of the microplanktonic groups to the immobilization and recycling of different nutrients.     

厦门湾营养盐长期动态变化与陆源污染关系分析

近年来快速城镇化和人类活动导致沿海地区营养盐含量显著增加,导致海湾富营养化现象日趋严重。了解水体营养盐含量分布特征与陆源污染之间的关系,是对海湾进行有效环境管理的前提。本研究以2010—2019年福建省厦门湾近岸海域水质监测数据为基础,分析长期性、季节性水质空间分布特征,并利用富营养化指数法对海湾富营养化状态进行评价,为氮、磷污染物治理提供措施建议。结果表明：厦门湾自2013年以来无机氮、无机磷含量波动降低,但同安湾无机磷含量近年来有明显增加。春季和秋季无机氮、无机磷含量明显高于夏季,不同季节氮、磷含量均呈现由湾内向湾外递减的分布趋势,反映出典型的陆源输入特征。硝酸盐氮是厦门湾无机氮的最主要成分,其与无机磷的比值普遍高于Redfield比值。无机氮、无机磷是导致九龙江口、西海域、同安湾富营养化指数较高的主要因子,受径流调控明显,无机磷在秋季还受到沿岸排污口的显著影响。厦门湾亟需加强对所有入海河流氮、磷污染的总量控制,建议强化沿岸排污口的管控。     

广西北海半岛夏季营养盐及水质状况分析

近年北部湾藻华灾害频发,为了解与藻华暴发密切相关的营养盐及水质状况,2020年8月作者对北部湾北海半岛铁山港、营盘、涠洲岛、斜阳岛及涠洲岛西部远岸海域共21个站位采集表层海水,分析营养盐含量和结构特征,并利用富营养化指数和有机污染指数对该海域水质进行等级划分与评价。结果表明：北海半岛海域DIN、PO₄-P和SiO₃-Si均值分别为0.210、0.021和0.270 mg/L。其中,铁山港营养盐由港内至港外呈递减趋势,营盘海域由近岸至远岸,DIN和SiO₃-Si含量先递减再增加,PO₄-P则表现为递增,涠洲岛海域及远岸各站位营养盐分布无明显特征。北海半岛海域N/P、Si/N和Si/P均值分别为11.8、1.7和14.6,显示47.6%海域为潜在N限制,而潜在P限制和Si限制海域均为9.5%;叶绿素a仅与COD显著相关,相关系数为0.475。调查海域富营养化指数均值1.82,以铁山港港内富营养化程度最高,由港内严重富营养至港外贫营养递减,营盘近岸7号站位中度富营养,其余76.2%调查站位仍处于贫营养水平;有机污染指数均值1.85,良好和较好水质共占38.1%,其余61.9%水质受到不同程度有机污染,亦以铁山港水质污染最为严重,重度污染仅在该海域发现。可见,北海半岛夏季表层海水以潜在N限制为主,铁山港和营盘近岸富营养化和有机污染较严重,其余站位基本良好,影响表层水体叶绿素a含量的主要因素是有机质,可能与海域微生物强烈降解作用相关。本研究可为北部湾海洋环境保护和赤潮研究提供基础环境数据。     

Lake Tutira: The use of phosphorus loadings in a management study

Abstract

Decisions on lake management will often have to be made when data are scarce. However, a nutrient budget based on limited data of varying reliability and on information from the literature may help considerably.

Lake Tutira's recreational uses are threatened by eutrophication. Artificial destratification is being used temporarily to protect the trout fishery. The annual phosphorus input to the lake was estimated from nutrient loading graphs, from scanty stream input data, and from land‐use information to be about 3100 kg (1.8 g·m^?2·y^?1).

The 5–10 times reduction in phosphorus loading apparently required to achieve mesotrophic to oligotrophic conditions establishes the need for major changes in the catchment. The phosphorus budget helped in assessing the relative importances of the input streams and evaluating stream diversion proposals. It suggested that phosphorus inputs came mostly from animal excreta, soil erosion, and fertiliser, and it provided support for farm management proposals. When the results of stream diversion and altered land management are known the phosphorus budget may help in deciding the optimum land area needed to be converted from pasture into forest.     

Tide- and rainfall-induced variations of physical and chemical parameters in a mangrove-depleted estuary of East Hainan (South China Sea)

The estuarine dynamics favoring the coexistence of mangroves, seagrass and corals at small river mouths are often poorly understood. We characterize the tidal, day/night and rainfall-induced short-term dynamics in salinity, pH, dissolved oxygen (DO), chlorophyll a (chl a), total suspended matter (TSM), water transparency, surface currents and dissolved nutrients (NO_x⁻, NH₄⁺, PO₄³⁻, Si(OH)₄) of the Wenchang/Wenjiao Estuary (East Hainan, tropical China). Samples were taken at three fixed sites along the estuary during 24 h spring tide cycles in different seasons. Salinity, DO, water transparency and pH generally increased seawards while nutrients decreased. All parameters varied with the tidal cycle, partially in interaction with the diel cycle. Nutrients, chl a and TSM usually fluctuated inversely with water level. Stratification was strong. Inflowing bottom water was of higher salinity, DO and pH and lower temperature and nutrient concentrations than the surface water. Tidal mixing provided regular ventilation of the estuary and limited eutrophication effects of nutrients from aquaculture, agriculture and urban effluents. Under dry weather conditions, the brackish-water lagoon functioned as a sink of nutrients due to efficient uptake by phytoplankton. Presently, the runoff from common intense rains in the watershed affects the estuary with little time delay due to terrestrial deforestation, channelization and loss of mangrove area. The frequency, strength and duration of intermittent estuarization of the back-reef areas have likely increased in the past and deteriorate present seagrass and coral health.     

Potential impacts of Three Gorges Dam in China on the ecosystem of East China Sea

The Changjiang River in China was dammed in 2003. The possible changes in matters fluxes from the river downstream after the completion of Three Gorges Dam and their potential impacts on the ecosystem of the East China Sea are discussed . The estuarine and coastal waters in the East China Sea were heavily fertilized by the inflow of nutrient-rich freshwater from the Changjiang River, which has led to severe eutrophication and frequent harmful algal blooms ,thus worsening the ecosystem health in this area. Analy- sis showed that the nutrient loadings are very likely to be reduced in the lower Changjiang River due to the construction of Three Gorges Dam. Especially for the total phosphorus, the discharges to the East China Sea will be reduced by one-third, which would relieve the severe eutrophication in this area. However, the expected decrease in the riverine silicate discharge would lead the ratio of silicon to nitrogen to be much less than 1 in the estuarine and coastal waters and thus may cause an elevation of flagellate growth. The changes in the annual water discharges and their seasonal distributions below the dam will be minor. Reduction of suspended particulate matter loading, due to the sedimentation behind the dam, will reduce the nutrient loadings of the particulate form especially for phosphorus, and decrease the turbidity of estuarine and coastal waters. On the other hand, this may enhance the erosion of the delta and the coasts as well as modifythe benthic ecosystem.     

Response of a benthic suspension feeder (Crassostrea virginica Gmelin) to three centuries of anthropogenic eutrophication in Chesapeake Bay

Biogenic reefs built by oysters and other suspension feeders are vital components of estuarine ecosystems. By consuming phytoplankton, suspension feeders act to suppress accumulation of organic matter in the water column. Nutrient loading increases the rate of primary production, thereby causing eutrophication. As suspension feeders consume more organic matter from increasing abundance of phytoplankton, their rate of growth should also increase if they are food limited. We show here that the eastern oyster, Crassostrea virginica (Gmelin), from St. Mary's and Patuxent rivers, Chesapeake Bay, grew faster during anthropogenic eutrophication relative to C. virginica before eutrophication. Growth of shell height, shell thickness and adductor muscle increased after eutrophication began in the late 18th century. After 1860, growth decreased, perhaps reflecting the negative effects of hypoxia, harmful algal blooms, disease and fishing on oyster growth. These results are consistent with the view that an increasing supply of phytoplankton resulting from eutrophication enhanced growth of C. virginica between 1760 and 1860, before oyster reefs were degraded by destructive fishing practices between 1870 and 1930. Alternative factors, such as changes in water temperature, salinity, and fishing are less likely to be responsible for this pattern. These results have implications for restoration of oyster reefs in order to mitigate the effects of eutrophication in estuaries, as well as the paleoecological relationship between suspension feeders and paleoproductivity.     

Physiology of Laminaria

Abstract. Sporophytes of Laminaria digitata and L. saccharina were collected from the shore at different times of year. Intact sporophytes of both species, and discs cut from L. digitata lamina tissue were maintained for several weeks in laboratory cultures under various nitrate, phosphate, temperature and daylength regimes. Substrate-saturated uptake rates of approximately 24 μgN g dry weight^-1 h^-1 from 20 μM nitrate and 8 μgP g dry weight^-1 h^-1 from 10 μM phosphate were more than sufficient to account for internal nitrogen and phosphorus accumulation. Other nitrogen sources - nitrite, ammonium and urea - were also taken up, independently of each other, and supported growth. During the late spring decline of ambient nutrient levels, when growth rates on the shore also decline markedly, enrichment with nitrate (15 μM) and phosphate (3μ) together prevented this decline and also maintained peak photosynthetic rates (net photosynthesis = 10.4 μlO₂ cm^-2 h^-1) which otherwise dropped to 4.5 μO₂ cm^-2 h^-1 over 47 days at ambient nutrient levels (0.5 μM nitrate and phosphate). Slow summer growth rates in June/July were enhanced to greater than spring peak values by combined nitrate (7.5 μM) and phosphate (1.8 μM) enrichment; neither was sufficient alone, although the individual nutrients were accumulated internally. A lesser, but significant enhancement was also achieved in September. In midwinter, nutrient enhancement itself (10.5 μM nitrate and 3.0 μM phosphate) had a small effect on growth rates only if summer water temperature (15°C) was used, but the dramatic effect of an increased photoperiod (7.5 to 17.5 h) was in excess of that expected for the increased radiant energy available. This was found to be due, at least in L. digitaia discs, to the re-establishment of a surface meristoderm in the dormant winter tissue; this was particularly active with high phosphate supply. Growth of the new lamina in January on the shore was much reduced if the old lamina was removed, although the time of initiation of new growth remained unchanged. In the laboratory, the old lamina was found to be a source of nitrogen for new lamina but not of fixed carbon or phosphorus. New lamina photosynthesis, manifest as mannitol accumulation, was directly proportional to phosphate supply up to at least 7.5 μM phosphate. Mannitol accumulation was then suppressed by a nitrate supply above 12 um, presumably by diversion of fixed carbon to other biosynthetic pathways.     

Analysis of primary production in the Seto Inland Sea, Japan, using a simple ecosystem model

A simple model of lower trophic level ecosystem has been created to analyze possible environmental control of primary production in eight sub-areas of the Seto Inland Sea. The primary production rates observed by Hashimotoet al. (1997a) in these sub-areas are well reproduced by the model, including horizontal processes such as horizontal transport of nutrients and vertical processes such as vertical mixing, light intensity and sinking of particulate matter. Without taking account of horizontal processes the model also successfully reproduces the observed primary production rates in some areas, but if fails to reproduce those in the others. This shows that the relative importance of the horizontal transport on the primary production differs are by area. Two time scales,T _z andT _H, are introduced to explain this difference.T _z is a vertical cycling time of material, which is defined as the time during which the stock of the material in the water column is utilized for primary production;T _H is the horizontal transit time of the material. The relative importance of the horizontal process is well explained by theT _H/T _z ratio; that is, the horizontal transport process is important in the areas where this ratio is small. Further the possible mechanisms of nutrient supply for the primary production in each sub-area are investigated using this model.     

Fluxes of riverine nutrient to the Zhujiang River Estuary and its potential eutrophication effect

The Zhujiang River Estuary is becoming eutrophic due to the impact of anthropogenic activities in the past decades. To understand nutrient dynamics and fluxes to the Lingdingyang water via four outlets(Humen,Jiaomen, Hongqimen and Hengmen), we investigated the spatial distribution and seasonal variation of dissolved nutrients in the Zhujiang River Estuary, based on fourteen cruises conducted from March 2015 to October 2017,covering both wet(April to September) and dry(October to March next year)...     

Spatial variation of nutrients and primary productivity in the Rufiji Delta mangroves,Tanzania

Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.