Eutrophication of freshwater and coastal marine ecosystems a global problem

GOAL, SCOPE AND BACKGROUND: Humans now strongly influence almost every major aquatic ecosystem, and their activities have dramatically altered the fluxes of growth-limiting nutrients from the landscape to receiving waters. Unfortunately, these nutrient inputs have had profound negative effects upon the quality of surface waters worldwide. This review examines how eutrophication influences the biomass and species composition of algae in both freshwater and costal marine systems. MAIN FEATURES: An overview of recent advances in algae-related eutrophication research is presented. In freshwater systems, a summary is presented for lakes and reservoirs; streams and rivers; and wetlands. A brief summary is also presented for estuarine and coastal marine ecosystems. RESULTS: Eutrophication causes predictable increases in the biomass of algae in lakes and reservoirs; streams and rivers; wetlands; and coastal marine ecosystems. As in lakes, the response of suspended algae in large rivers to changes in nutrient loading may be hysteretic in some cases. The inhibitory effects of high concentrations of inorganic suspended solids on algal growth, which can be very evident in many reservoirs receiving high inputs of suspended soils, also potentially may occur in turbid rivers. Consistent and predictable eutrophication-caused increases in cyanobacterial dominance of phytoplankton have been reported worldwide for natural lakes, and similar trends are reported here both for phytoplankton in turbid reservoirs, and for suspended algae in a large river CONCLUSIONS: A remarkable unity is evident in the global response of algal biomass to nitrogen and phosphorus availability in lakes and reservoirs; wetlands; streams and rivers; and coastal marine waters. The species composition of algal communities inhabiting the water column appears to respond similarly to nutrient loading, whether in lakes, reservoirs, or rivers. As is true of freshwater ecosystems, the recent literature suggests that coastal marine ecosystems will respond positively to nutrient loading control efforts. RECOMMENDATIONS AND OUTLOOK: Our understanding of freshwater eutrophication and its effects on algal-related water quality is strong and is advancing rapidly. However, our understanding of the effects of eutrophication on estuarine and coastal marine ecosystems is much more limited, and this gap represents an important future research need. Although coastal systems can be hydrologically complex, the biomass of marine phytoplankton nonetheless appears to respond sensitively and predictably to changes in the external supplies of nitrogen and phosphorus. These responses suggest that efforts to manage nutrient inputs to the seas will result in significant improvements in coastal zone water quality. Additional new efforts should be made to develop models that quantitatively link ecosystem-level responses to nutrient loading in both freshwater and marine systems.     

Complex interactions between autotrophs in shallow marine and freshwater ecosystems: implications for community responses to nutrient stress

The relative biomass of autotrophs (vascular plants, macroalgae, microphytobenthos, phytoplankton) in shallow aquatic ecosystems is thought to be controlled by nutrient inputs and underwater irradiance. Widely accepted conceptual models indicate that this is the case both in marine and freshwater systems. In this paper we examine four case studies and test whether these models generally apply. We also identify other complex interactions among the autotrophs that may influence ecosystem response to cultural eutrophication. The marine case studies focus on macroalgae and its interactions with sediments and vascular plants. The freshwater case studies focus on interactions between phytoplankton, epiphyton, and benthic microalgae. In Waquoit Bay, MA (estuary), controlled experiments documented that blooms of macroalgae were responsible for the loss of eelgrass beds at nutrient-enriched locations. Macroalgae covered eelgrass and reduced irradiance to the extent that the plants could not maintain net growth. In Hog Island Bay, VA (estuary), a dense lawn of macroalgae covered the bottom sediments. There was reduced sediment-water nitrogen exchange when the algae were actively growing and high nitrogen release during algal senescence. In Lakes Brobo (West Africa) and Okeechobee (FL), there were dramatic seasonal changes in the biomass and phosphorus content of planktonic versus attached algae, and these changes were coupled with changes in water level and abiotic turbidity. Deeper water and/or greater turbidity favored dominance by phytoplankton. In Lake Brobo there also was evidence that phytoplankton growth was stimulated following a die-off of vascular plants. The case studies from Waquoit Bay and Lake Okeechobee support conceptual models of succession from vascular plants to benthic algae to phytoplankton along gradients of increasing nutrients and decreasing under-water irradiance. The case studies from Hog Island Bay and Lake Brobo illustrate additional effects (modified sediment-water nutrient fluxes, allelopathy or nutrient release during plant senescence) that could play a role in ecosystem response to nutrient stress.     

Phytoplankton can bypass nutrient reductions in eutrophic coastal water bodies

The EU-water framework directive aims at nutrient reductions, since anthropogenically induced eutrophication is a major threat for coastal waters. However, phytoplankton biomass in southern Baltic Sea coastal water bodies (CWB) remains high and the underlying mechanisms are not well understood. Therefore, a CWB data set was analysed regarding changes in phytoplankton biomass and nutrient concentration of nitrogen (N) and phosphorus (P) from 2000 to 2014. It was expected to find imbalances between produced phytoplankton biomass and total nutrient concentrations. Inner CWB were cyanobacteria-dominated and showed up to five times higher chlorophyll a-concentrations compared to outer CWB with similar total phosphorus-concentrations. Phytoplankton tended to be P-limited during spring and N-limited during summer. Phytoplankton biomass and nutrient concentrations were even higher during very humid years, which indicated a close coupling of the CWB with their catchment areas. This study suggests that re-mesotrophication efforts need to consider the importance of changed phytoplankton composition and nutrient availabilities.     

Distribution and partitioning of phosphorus in solid waste and sediments from drainage canals in the industrial belt of Delhi, India

Phosphorus is an essential and often limiting nutrient in both marine and freshwater ecosystems. However, its oversupply is of great concern in many environments due to its role in eutrophication. The concentration and distribution of sediment bound phosphorus species not only record its input into the environment, but also suggest their possible sources. It is recognized that the features of phosphorus behaviour have not been extensively studied in urban environments. In this study, phosphorus in solid waste and sediments from drainage canals within the industrial belt of Delhi were fractionated into five operationally defined forms, i.e., exchangeable or loosely sorbed phosphorus (Exch-P), Fe-bound phosphorus (Fe-P), authigenic apatite, CaCO3-bound phosphorus and biogenic apatite (Acet-P), detrital apatite (Det-P) and organic-bound phosphorus (Org-P), in order to assess the potential bioavailability status in these systems.     

Effects of harvest regime and water depth on nutrient recovery from swine wastewater by growing Spirodela oligorrhiza

Harvest regime and water depth were investigated to determine their effects on nutrient recovery from swine wastewater by a Spirodela oligorrhiza system. The results show that harvesting less duckweed at shorter intervals favored nutrient removal and total biomass production. Harvesting 20% of duckweed twice a week led to 66.3 and 109.4% higher total nitrogen and total phosphorus removals, respectively, and a duckweed production of 20.0 g fresh biomass/m2 x d--39.6% higher than that of harvesting 80% of duckweed once every 4 weeks. The water depth of duckweed system was of great importance to total nutrient removal. At the water depth of 40 cm, total nitrogen and total phosphorus removals were 2.05 and 2.16 times higher, respectively, than those at the water depth of 10 cm. However, because of the larger amount of nutrients in a deeper system, it took a longer time for the nutrient concentrations to decrease.     

Abrupt biological response to hydrologic and land-use changes in Lake Apopka, Florida, USA

Lake Apopka is a shallow, hypereutrophic lake in north-central Florida that experienced an abrupt shift in primary producer community structure (PPCS) in 1947. The PPCS shift was so abrupt anecdotal accounts report that dominant, submersed aquatic vegetation was uprooted by a hurricane in 1947 and replaced by phytoplankton within weeks. Here we propose two hypotheses to explain the sudden shift to phytoplankton. First, hydrologic modification of the drainage basin in the late 1800s lowered the lake level ca. 1.0 m, allowing the ecosystem to accommodate moderate, anthropogenic nutrient enrichment through enhanced production in the macrophyte community. Second, additional hydrologic changes and large-scale agricultural development of floodplain wetlands began in 1942 and altered the pattern and scale of phosphorus loading to the lake that triggered the rapid shift to phytoplankton dominance in 1947. Historic land-use changes and paleolimnological data on biological responses to nutrient loading support these hypotheses.     

Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs

Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N₂ allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.     

Salinity and nutrient modulate soil bacterial communities in the coastal wetland of the Yellow River Delta,China

The Yellow River Delta is the largest and youngest estuarine and coastal wetland in China and is experiencing the most active interactions of seawater and freshwater in the world. Bacteria played multifaceted influence on soil biogeochemical processes, and it was necessary to investigate the intermodulation between the soil factors and bacterial communities. Soil samples were collected at sites with different salinity degree, vegetations, and interference. The sequences of bacilli were tested using 16S rRNA sequencing method and operational taxonomic units were classified with 97% similarity. The soil was highly salinized and oligotrophic, and the wetland was nitrogen-restricted. Redundancy analysis suggested that factors related with seawater erosion were principal to drive the changes of soil bacterial communities and then the nutrient level and human disturbance. A broader implication was that, in the early succession stages of the coastal ecosystem, seawater erosion was the key driver of the variations of marine oligotrophic bacterial communities, while the increasing nutrient availability may enhance in the abundance of the riverine copiotrophs in the late stages. This study provided new insights on the characteristics of soil bacterial communities in estuarine and coastal wetlands.

     

Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems

In the mid-1800s, the agricultural chemist Justus von Liebig demonstrated strong positive relationships between soil nutrient supplies and the growth yields of terrestrial plants, and it has since been found that freshwater and marine plants are equally responsive to nutrient inputs. Anthropogenic inputs of nutrients to the Earth's surface and atmosphere have increased greatly during the past two centuries. This nutrient enrichment, or eutrophication, can lead to highly undesirable changes in ecosystem structure and function, however. In this paper we briefly review the process, the impacts, and the potential management of cultural eutrophication in freshwater, marine, and terrestrial ecosystems. We present two brief case studies (one freshwater and one marine) demonstrating that nutrient loading restriction is the essential cornerstone of aquatic eutrophication control. In addition, we present results of a preliminary statistical analysis that is consistent with the hypothesis that anthropogenic emissions of oxidized nitrogen could be influencing atmospheric levels of carbon dioxide via nitrogen stimulation of global primary production.     

Effects of major nutrient additions on metal uptake in phytoplankton

We examined the influences of major nutrients (N, P, Si) on the accumulation of three trace metals [Cd, Se(IV), and Zn] in four species of marine phytoplankton (diatom, green alga, dinoflagellate, prasinophyte). Relative metal uptake was quantified by the kinetic measurements of metal concentration factor over a short exposure period. Our study demonstrated that nutrient addition significantly influenced the metal uptake rate and the cell growth rate in all four phytoplankton species. An increase in ambient N concentration considerably enhanced metal uptake by the cells. The dry weight concentration factor increased by 2.4-14.9 times for Cd, 1.1-4.0 times for Se, and 1.1-5.4 times for Zn in all four phytoplankton species with an addition of 176.4 microM N. The effects of P or Si addition on metal uptake and cell growth were less pronounced than the effects of N addition. Under most circumstances the rate of metal uptake increased exponentially with increasing cell growth rate constant. Only Se(IV) uptake in the diatom Phaeodactylum tricornutum was not correlated with cell growth rate. Se(IV) was not accumulated by the green algae Chlorella autotrophica at a high P concentration (7.2 microM), but appreciable accumulation was documented in cells inoculated without P addition. Our study therefore demonstrated that nutrient enrichments in many coastal waters can considerably affect trace metal uptake in phytoplankton and presumably metal trophic transfer in marine food chains.     

Nutrient dynamics in shallow lakes of northern greece

GOAL, SCOPE, BACKGROUND: Shallow lakes display a number of features that set them apart from the more frequently studied deeper systems. The majority of lakes in Northern Greece are small to moderate in size with a relatively low depth and are considered as sites of high value of the wetland habitat. However, the water quality of these lakes has only been evaluated segmentally and occasionally. OBJECTIVE: The objectives of this study were to thoroughly investigate nitrogen and phosphorus speciation in lakes of a high ecological significance located in N. Greece, in order to evaluate their eutrophication status and possible nutrient limitation factors, and to investigate the main factors/sources that affect the water quality of these systems. METHODS: An extensive survey was carried out during the period from 1998-1999. Water samples were collected on a monthly basis from lakes Koronia, Volvi, Doirani, Mikri Prespa and Megali Prespa located in N. Greece. Water quality parameters (temperature, dissolved oxygen, pH and conductivity), organic indices (COD, BOD5), and N- and P-species (NO3(-), NO2(-), NH4(+), and PO4(3-), Kieldahl nitrogen and acid-hydrolysable phosphorus) were determined according to standard methods for surface water. Statistical treatment of the data was employed. RESULTS AND CONCLUSIONS: The physicochemical parameters determined in the lakes studied revealed a high temporal variation. The trophic state of the lakes ranged from meso- to hypertrophic. The nutrient limiting factor varied among lakes suggesting either P-limitation conditions or mixed conditions changing from P- to N-limitation throughout the year. Urban/industrial activities and agricultural runoff are the major factors affecting all lakes, although with a varying contribution. RECOMMENDATION AND OUTLOOK: This lake-specific research offers valuable information about water quality and nutrient dynamics in lakes of significant ecological value located in N. Greece that can be useful for an effective pollution control/management of these systems. Due to the large intra-annual variability of certain physicochemical parameters, a properly designed monitoring program of lake water is recommended.     

Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management

By mainly targeting larger predatory fish, commercial fisheries have indirectly promoted rapid increases in densities of their prey; smaller predatory fish like sprat, stickleback and gobies. This process, known as mesopredator release, has effectively transformed many marine offshore basins into mesopredator-dominated ecosystems. In this article, we discuss recent indications of trophic cascades on the Atlantic and Baltic coasts of Sweden, where increased abundances of mesopredatory fish are linked to increased nearshore production and biomass of ephemeral algae. Based on synthesis of monitoring data, we suggest that offshore exploitation of larger predatory fish has contributed to the increase in mesopredator fish also along the coasts, with indirect negative effects on important benthic habitats and coastal water quality. The results emphasize the need to rebuild offshore and coastal populations of larger predatory fish to levels where they regain their control over lower trophic levels and important links between offshore and coastal systems are restored.     

Seasonal variations of nitrogen and phosphorus retention in an agricultural drainage river in East China

Background, aim, and scope  

Riverine retention decreases loads of nitrogen (N) and phosphorus (P) in running water. It is an important process in nutrient cycling in watersheds. However, temporal riverine nutrient retention capacity varies due to changes in hydrological, ecological, and nutrient inputs into the watershed. Quantitative information of seasonal riverine N and P retention is critical for developing strategies to combat diffuse source pollution and eutrophication in riverine and coastal systems. This study examined seasonal variation of riverine total N (TN) and total P (TP) retention in the ChangLe River, an agricultural drainage river in east China.     

The perverse fisheries consequences of mosquito net malaria prophylaxis in East Africa

Malaria is a serious global health issue, with around 200 million cases per year. As such, great effort has been put into the mass distribution of bed nets as a means of prophylaxis within Africa. Distributed mosquito nets are intended to be used for malaria protection, yet increasing evidence suggests that fishing is a primary use for these nets, providing fresh concerns for already stressed coastal ecosystems. While research documents the scale of mosquito net fisheries globally, no quantitative analysis of their landings exists. The effects of these fisheries on the wider ecosystem assemblages have not previously been examined. In this study, we present the first detailed analysis of the sustainability of these fisheries by examining the diversity, age class, trophic structure and magnitude of biomass removal. Dragnet landings, one of two gear types in which mosquito nets can be utilised, were recorded across ten sites in northern Mozambique where the use of Mosquito nets for fishing is common. Our results indicate a substantial removal of juveniles from coastal seagrass meadows, many of which are commercially important in the region or play important ecological roles. We conclude that the use of mosquito nets for fishing may contribute to food insecurity, greater poverty and the loss of ecosystem functioning.

     

生物脱氮除磷工艺中的微生物及其相互关系

本文着重对近年来脱氮除磷微生物学方面的研究进展进行了综述 ,分析了生物脱氮除磷反应器中各类功能微生物间的相互作用关系 ,营养物代谢机理和对处理效率的贡献 ,讨论了脱氮除磷生物学应深入研究的一些问题。     

浮萍植物在污水处理中的应用研究进展

浮萍科植物是漂浮生长在水流相对平缓的湖泊河湾水面上植物类群,整个植株完全退化为一个呈圆形或椭圆形的叶状体,主要是通过根或叶状体从水中吸收所需的氮磷等各种营养物质.浮萍科植物的氮磷含量和生长速率高并可以耐受多种污水条件,因此这个类群是污水处理生态工程中重要的水生植物类群.以浮萍为主的污水处理系统已得到较多的研究和应用,这类系统最大特点是浮萍的生长可以大量吸收污水中的氮磷,从而具有较高的氮磷去除率,同时生成的生物量可多种方式利用.因此利用这类系统对污水进行氮磷的处理与转化,并将生成的浮萍生物量适当地资源化利用是未来的发展方向.     

Effects of land use and land cover, stream discharge, and interannual climate on the magnitude and timing of nitrogen, phosphorus, and organic carbon concentrations in three coastal plain watersheds.

In-stream nitrogen, phosphorus, organic carbon, and suspended sediment concentrations were measured in 18 subbasins over 2 annual cycles to assess how land use and land cover (LULC) and stream discharge regulate water quality variables. The LULC was a primary driver of in-stream constituent concentrations and nutrient speciation owing to differences in dominant sources and input pathways associated with agricultural, urban, and forested land uses. Stream discharge was shown to be a major factor that dictated not only the magnitude of constituent concentrations, but also the chemical form. In high discharge agricultural subbasins, where nitrate was the dominant nitrogen form, there was a negative correlation between discharge and nitrate concentration indicating groundwater inputs as the dominant pathway. In urban settings, however, nitrate was positively correlated with discharge, and, in forested subwatersheds, where dissolved organic nitrogen (DON) was the dominant nitrogen form, there was a positive correlation between discharge and DON, indicating washoff from the watershed as the dominant input pathway. Similarly, phosphorus concentrations were strongly regulated by LULC, discharge, and seasonality. This comparative study highlights that different mechanisms regulate different forms of nitrogen, phosphorus, and carbon, and thus field programs or water quality models used for regulatory purposes must assess these nutrient forms to accurately apply management plans for nutrient reductions.     

Management of marine cage aquaculture

Goal, Scope and Background Marine cage aquaculture produces a large amount of waste that is released directly into the environment. To effectively manage the mariculture environment, it is important to determine the carrying capacity of an aquaculture area. In many Asian countries trash fish is dominantly used in marine cage aquaculture, which contains more water than pellet feed. The traditional nutrient loading analysis is for pellet feed not for trash fish feed. So, a more critical analysis is necessary in trash fish feed culturing areas. Methods Corresponding to FCR (feed conversion rate), dry feed conversion rate (DFCR) was used to analyze the nutrient loadings from marine cage aquaculture where trash fish is used. Based on the hydrodynamic model and the mass transport model in Xiangshan Harbor, the relationship between the water quality and the waste discharged from cage aquaculture has been determined. The environmental carrying capacity of the aquaculture sea area was calculated by applying the models noted above. Results Nitrogen and phosphorus are the water quality parameters considered in this study. The simulated results show that the maximum nitrogen and phosphorus concentrations were 0.216 mg/L and 0.039 mg/L, respectively. In most of the sea area, the nutrient concentrations were higher than the water quality standard. The calculated environmental carrying capacity of nitrogen and phosphorus in Xiangshan Harbor were 1,107.37 t/yr and 134.35 t/yr, respectively. The waste generated from cage culturing in 2000 has already exceeded the environmental carrying capacity. Discussion Unconsumed feed has been identified as the most important origin of all pollutants in cage culturing systems. It suggests the importance of increasing the feed utilization and improving the feed composition on the basis of nutrient requirement. For the sustainable development of the aquaculture industry, it is an effective management measure to keep the stocking density and pollution loadings below the environmental carrying capacity. Conclusions The DFCR-based nutrient loadings analysis indicates, in trash fish feed culturing areas, that it is more critical and has been proved to be a valuable loading calculation method. The modeling approach for Xiangshan Harbor presented in this paper is a cost-effective method for assessing the environmental impact and determining the capacity. Carrying capacity information can give scientific suggestions for the sustainable management of aquaculture environments. Recommendations and Perspectives It has been proved that numerical models were convenient tools to predict the environmental carrying capacity. The development of models coupled with dynamic and aquaculture ecology is a requirement of further research. Such models can also be useful in monitoring the ecological impacts caused by mariculture activities. ESS-Submission Editor: Hailong Wang (hailong.wang@ensisjv.com)     

Mitigation of eutrophication caused by wastewater discharge: A simulation-based approach

Mitigation of eutrophication, intensified by excessive nutrient load discharge in wastewaters regulated by restrictive legal requirements, remains one of today’s most important global problems. Despite implementation of the Water Framework Directive, the Urban Wastewater Directive and the HELCOM recommendations, the actual condition of surface water is still not satisfactory. In response to the above, the study presents an alternative approach for surface water protection against eutrophication based on the selection of appropriate nutrient removal technologies. An activated sludge model simulation was used to enable the identification of environmentally justified nutrient removal systems with lowest eutrophication potential of treated wastewater conditioned by bioavailable nutrient forms content. Based on the outcome of the study, the 3-stage Bardenpho system was identified as the most efficient for bioavailable phosphorus removal, while the Johannesburg system proved to have the highest efficiency for bioavailable nitrogen removal. The proposed eutrophication mitigation approach underlines the need for a reconsideration of current legal regulations which ignore nutrient bioavailability and key eutrophication limiting factors.     

Verification of the silica deficiency hypothesis based on biogeochemical trends in the aquatic continuum of Lake Biwa-Yodo River-Seto Inland Sea, Japan

The silica deficiency hypothesis holds that increases of still waters caused by hydraulic alterations and high nitrogen (N) and phosphorus (P) discharges enhance the growth of freshwater diatoms, which take up the dissolved silicate (DSi) supplied by natural weathering. The consequent decrease in the DSi supply to the sea is advantageous to flagellates (nonsiliceous and potentially harmful) but not to diatoms (siliceous and mostly benign) in coastal marine ecosystems. Verification of this hypothesis has been hampered by lack of relevant data, particularly in Asia. We investigated the aquatic continuum composed of Lake Biwa, the Yodo River, and the Seto Inland Sea, Japan, where the natural conditions make the silica deficiency less likely to emerge due to the inherently rich supply of DSi. The results showed that the silica was retained both in the lake and nearby the estuary. The relative dominance of diatom and flagellates could not be explained solely by the stoichiometric arguments but by the supportive discussion on the difference of their behavioral characteristics and the process nearby the estuary, where direct inputs of N and P and effluent Si enhanced diatom bloom, even though the Si/N ratio was lowered in the upstream reservoir. Thus the retention of DSi occurred in two places: in the lake and nearby the estuary, where the other N and P are loaded directly. The rate of DSi retention correlated with socio-economic changes, such as rapid economic growth in the 1960s and mitigations implemented after the 1980s. Sensitivity of this continuum to the Si processes suggests the global significance of this hypothesis.