Opportunities and challenges for managing nitrogen in urban stormwater: A review and synthesis

Although nitrogen (N) is prevalent in urban stormwater, regulation of this pollutant has occurred only more recently. This paper reviews the concerns over N in urban stormwater, mechanisms and design enhancements for N uptake and denitrification through various stormwater control measures (SCMs), and presents opportunities to integrate this current knowledge into the regulatory framework. A survey of personnel directly involved in various aspects of US state and territory NPDES programs revealed that the top three pollutants of concern were total suspended solids (TSS), pathogens and bacteria, and total phosphorus (TP). Surprisingly, nitrate (NO₃^?) was of little concern among the survey respondents, with 3.9% giving it the highest level of concern, 2.0% ranking it second, and 6.0% ranking it third. When asked which strategies were currently used in their geographic area for stormwater management, the most common results were wet ponds and dry ponds. At the same time, wet ponds and dry ponds were recognized as less effective practices to manage stormwater.A review of current literature reveals that several alternative SCMs, such as bioretention, filters, and wetlands, show greater promise in their ability to remove N from stormwater than more conventional practices such as dry ponds and wet ponds. Enhanced N removal via denitrification and plant uptake is often observed under the combination of aerobic followed by sustained anoxic conditions, the presence of a carbon source (organic material), and the presence of mature, dense vegetation.Given the lack of concern or awareness of local officials related to N loading from urban stormwater, and variation in the efficacy of various SCMs, it is not surprising that regulators remain focused on conventional dry pond and wet pond control measures. More needs to be done to quantify the impact of urban sources of N on water quality and aquatic ecosystems. In addition, greater focus needs to be placed on the development of design criteria for SCMs, such as bioretention, filters, and constructed wetlands, which show more promise for N removal.     

Ecological risk assessment of urban stormwater ponds: Literature review and proposal of a new conceptual approach providing ecological quality goals and the associated bioassessment tools

Stormwater ponds are a common feature of the urban landscape in many countries with advanced stormwater management. Built to control the impacts of urbanization in the form of increased runoff flows, volumes and pollution loads, stormwater ponds are exposed to strong anthropogenic pressures. Meanwhile, as open water systems, they represent new aquatic habitats potentially enhancing the biodiversity of urban areas and balancing the transformation of original ecosystems existing prior to urbanization. In the current context of sustainable development, assessing the ecological risks of stormwater ponds serving as aquatic habitats is therefore crucial for ensuring both the preservation and rehabilitation of biodiversity in urban areas. During the last decade, ecological risk assessments applied to stormwater ponds lacked adoption of integrated interdisciplinary approaches. This prevented advances in developing adaptive methodologies for assessing the ecological quality of stormwater ponds and for providing quality objectives for the management of these facilities. Also, the application of established integrated assessment methodologies, such as the Sediment Quality Triad widely used in North America, based on comparisons with reference sites, is challenged by the man-made features of urban stormwater ponds. The search for a more specific and effective methodology led to the proposal of supplementing the Sediment Quality Triad with the Oligochaete methodology, which was developed and standardized in France for determining the biological status of sediments in stagnant water ecosystems. The benefits of this approach are discussed in a conceptual framework providing ecological quality goals for urban stormwater ponds.     

Distinct Optical Chemistry of Dissolved Organic Matter in Urban Pond Ecosystems

Urbanization has the potential to dramatically alter the biogeochemistry of receiving freshwater ecosystems. We examined the optical chemistry of dissolved organic matter (DOM) in forty-five urban ponds across southern Ontario, Canada to examine whether optical characteristics in these relatively new ecosystems are distinct from other freshwater systems. Dissolved organic carbon (DOC) concentrations ranged from 2 to 16 mg C L^-1 across the ponds with an average value of 5.3 mg C L^-1. Excitation-emission matrix (EEM) spectroscopy and parallel factor analysis (PARAFAC) modelling showed urban pond DOM to be characterized by microbial-like and, less importantly, by terrestrial derived humic-like components. The relatively transparent, non-humic DOM in urban ponds was more similar to that found in open water, lake ecosystems than to rivers or wetlands. After irradiation equivalent to 1.7 days of natural solar radiation, DOC concentrations, on average, decreased by 38% and UV absorbance decreased by 25%. Irradiation decreased the relative abundances of terrestrial humic-like components and increased protein-like aspects of the DOM pool. These findings suggest that high internal production and/or prolonged exposure to sunlight exerts a distinct and significant influence on the chemistry of urban pond DOM, which likely reduces its chemical similarity with upstream sources. These properties of urban pond DOM may alter its biogeochemical role in these relatively novel aquatic ecosystems.     

Does the morphology of beaver ponds alter downstream ecosystems?

Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year. Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual hydrologic variation.     

Stormwater ponds and biofilters for large urban sites: Modeled arrangements that achieve the phosphorus reduction target for Boston's Charles River, USA

Urban rivers daily receive tons of phosphorus and other pollutants from stormwater generated by impervious surfaces. Constructed detention ponds and biofiltration cells (biofilters) are often effective for localized stormwater treatment, yet less is known about their effectiveness for large built areas. Our goals were to assess stormwater phosphorus-removal relative to total percent cover, number, size, and configuration of detention ponds and biofilters. Two approximately 200-ac. (80 ha) industrial and institutional sites near Boston's Charles River containing diverse smaller drainages, land uses, and runoff sources were analyzed. Using the model WinSLAMM, P-reduction percents were calculated and compared for detention ponds (1-40 per site; covering 5-15% of their drainage areas) and biofilters (two sizes, with and without underdrains; ∼900-4300 per site; 5-10% cover). The government's proposed TMDL target of 65% P-reduction was only achieved with designs that treated 100% of urban land with a pond or biofilter. The 65% target was met by a single pond covering 5% of the site and by several multi-pond or biofilter arrangements with coverage ranging from 5% to 10%. A stringent water quality goal of 75% P-reduction was also attained with certain consolidated and dispersed pond and biofilter designs. Configuration of treatment landscapes appeared to be more important than total treatment area. Results were generally similar for the large institutional and industrial sites. Stormwater P-reduction goals can be creatively met with diverse, realistic land allocations for ponds and biofilters, which also provide enhanced aesthetics, recreation opportunities, and other benefits beyond water quality.     

Unravelling the correlates of species richness and ecological uniqueness in a metacommunity of urban pond insects

City ponds have the potential to harbour a rich biodiversity of aquatic insects despite being located in an urban landscape. However, our current knowledge on the correlates of pond biodiversity is limited and even less is known about the factors that influence the ecological uniqueness of urban ponds. The multiple environmental gradients, at different spatial scales, that may affect biodiversity and ecological uniqueness of urban ponds can thus be seen both as an opportunity and as a challenge for a study. In this study, we aimed to fill this gap by focusing on aquatic insect assemblages in 51 ponds in the Swedish city of Stockholm, using a metacommunity perspective. We found that species richness was primarily determined by the density of aquatic insects, water depth and proportion of buildings around the pond. The uniqueness of ponds was estimated as local contributions to beta diversity (LCBD), and it was primarily related to the proportion of arable land and industry around the ponds. With regard to the metacommunity we found two interesting patterns. First, there was a negative relationship between richness and LCBD. Second, biodiversity was spatially independent, suggesting that spatially-patterned dispersal did not structure species richness or LCBD. These last two patterns are important when considering conservation efforts of biodiversity in city ponds. We hence suggest that the conservation of insect biodiversity in urban pond should consider the surroundings of the ponds, and that high-richness ponds are not necessarily those that require most attention because they are not ecologically the most unique.     

Urban ponds as an aquatic biodiversity resource in modified landscapes

Urbanization is a global process contributing to the loss and fragmentation of natural habitats. Many studies have focused on the biological response of terrestrial taxa and habitats to urbanization. However, little is known regarding the consequences of urbanization on freshwater habitats, especially small lentic systems. In this study, we examined aquatic macro‐invertebrate diversity (family and species level) and variation in community composition between 240 urban and 782 nonurban ponds distributed across the United Kingdom. Contrary to predictions, urban ponds supported similar numbers of invertebrate species and families compared to nonurban ponds. Similar gamma diversity was found between the two groups at both family and species taxonomic levels. The biological communities of urban ponds were markedly different to those of nonurban ponds, and the variability in urban pond community composition was greater than that in nonurban ponds, contrary to previous work showing homogenization of communities in urban areas. Positive spatial autocorrelation was recorded for urban and nonurban ponds at 0–50 km (distance between pond study sites) and negative spatial autocorrelation was observed at 100–150 km and was stronger in urban ponds in both cases. Ponds do not follow the same ecological patterns as terrestrial and lotic habitats (reduced taxonomic richness) in urban environments; in contrast, they support high taxonomic richness and contribute significantly to regional faunal diversity. Individual cities are complex structural mosaics which evolve over long periods of time and are managed in diverse ways. This facilitates the development of a wide range of environmental conditions and habitat niches in urban ponds which can promote greater heterogeneity between pond communities at larger scales. Ponds provide an opportunity for managers and environmental regulators to conserve and enhance freshwater biodiversity in urbanized landscapes whilst also facilitating key ecosystem services including storm water storage and water treatment.     

Garden pond diversity: Opportunities for urban freshwater conservation

Urbanisation is increasing globally, degrading terrestrial and freshwater habitats and reducing faunal and floral richness. Whilst the potential for garden ponds to serve as important biodiversity resources in urban areas has been documented in a limited number of studies, quantifying the contribution of garden ponds to urban freshwater diversity has been largely neglected. This study aims to quantify the taxonomic richness, community composition and conservation value of aquatic macroinvertebrates in domestic garden and non-urban ponds. Taxonomic richness was significantly lower in garden ponds than non-urban ponds at an alpha and gamma scale. A greater richness of Odonata, Coleoptera, Gastropoda and Hemiptera were recorded in non-urban ponds. Garden ponds were found to support compositionally different macroinvertebrate communities compared to non-urban ponds, influenced by variation in water depth and conductivity. A total of 23 taxa were recorded from garden ponds only. Non-urban ponds had a significantly higher conservation value compared to garden ponds (87% of garden ponds were of low or moderate conservation value, while only 35% of non-urban ponds were in these categories). Although garden ponds currently support limited macroinvertebrate diversity and have lower conservation value, they contribute to the regional species pool and their potential to limit future urban biodiversity loss is significant. Given their high abundance and popularity within the urban landscape, clear guidance is required for pond-owners on how to best manage garden ponds to support and sustain biodiversity. For this to be achieved, research is required to increase fundamental understanding of urban pond ecology, and the development of evidence led garden pond management practices.     

Distribution of Plesiomonas shigelloides in various components of pond ecosystems in Dhaka, Bangladesh.

Plesiomonas shigelloides is considered to be a waterborne agent of human gastroenteritis. An ecological study was carried out in five ponds in Dhaka city over a period of one year to elucidate the distribution and seasonality of this organism in various components of pond ecosystems. Samples were collected from hydrophytes, water, phytoplankton and sediment every 15 days over 12 months and cultured for P. shigelloides. P. shigelloides was isolated from a total of 120 samples including 25 (20.8%), 16 (13.3%), 22 (18.3%) and 35 (29.2%) of hydrophytes, water, phytoplankton and sediment samples, respectively. Distinct seasonal patterns of isolation of P. shigelloides were observed in the four components with two distinct peaks. The highest peaks were observed in hydrophytes and water samples in May and in phytoplankton and sediment in November. P. shigelloides was isolated from all components from all ponds during the study period. These results suggest that P. shigelloides is an autochthonous member in the freshwater pond ecosystems in Dhaka, Bangladesh.     

亚热带河口陆基养虾塘水体溶解性碳浓度及沉积物-水界面碳通量时空动态特征

以福建闽江和九龙江河口陆基养虾塘为研究对象,通过野外原位观测和室内模拟培养实验,开展了河口陆基养虾塘养殖期间水体溶解性有机碳(DOC)和溶解性无机碳(DIC)及养虾塘沉积物-水界面碳交换通量变化特征的研究。结果表明:时间变化上,养虾塘水体溶解性碳浓度及沉积物-水界面碳通量在闽江河口呈现8月中旬10月中旬6月中旬的特征,在九龙江河口表现为随养殖阶段推移而增加的趋势;空间变化上,闽江河口养虾塘水体溶解性碳浓度及沉积物-水界面碳通量显著高于九龙江河口;沉积物释放溶解性碳速率与水体溶解性碳浓度呈现显著正相关关系,沉积物碳释放过程是引起养虾塘水体溶解性碳浓度时空变化的重要因素。表明河口区水产养虾塘碳循环研究时需考虑不同形态碳生物地球化学循环的时空差异性。     

Promoting dragonfly diversity in cities: major determinants and implications for urban pond design

Urbanisation is increasing and it is essential to integrate biodiversity into the spatial planning of urban areas. This requires deeper understanding of biodiversity patterns in cities. We investigated which habitat variables are major determinants of dragonfly diversity and species assemblage structure in the municipal area of Dortmund (Germany). We sampled dragonfly larvae in 33 ponds situated in city parks, commercial, residential and agricultural areas. We recorded 30 autochthonous dragonfly species with species richness ranging from zero to 17. Additionally, we surveyed a set of environmental variables including habitat size, water level, pond structures and vegetation as well as surrounding landscape and potential disturbances like waterfowl and fish. Multivariate methods were used to identify the major determinants of dragonfly diversity, abundance and assemblage structure. Analysis indicated that diversity of aquatic and terrestrial vegetation affected dragonfly diversity positively. City park ponds had low diversity, but Ischnura elegans was obviously promoted by the specific park pond conditions, including high waterfowl density. We found five assemblages mostly determined by generalistic species which were related to different pond types. Moderately disturbed ruderal and pioneer ponds in residential and agricultural areas also contained increased numbers of rare species. Our results indicate that urban ponds may have a great value for maintaining biodiversity, but various disturbances have negative impact. To promote urban biodiversity we suggest a natural design of well-vegetated ponds as well as a high diversity of different pond types and particularly a more-natural redesign of city park ponds.     

Unique microbiome in organic matter–polluted urban rivers

Approximately half of the global annual production of wastewater is released untreated into aquatic environments, which results in worldwide organic matter pollution in urban rivers, especially in highly populated developing countries. Nonetheless, information on microbial community assembly and assembly-driving processes in organic matter–polluted urban rivers remains elusive. In this study, a field study based on water and sediment samples collected from 200 organic matter–polluted urban rivers of 82 cities in China and Indonesia is combined with laboratory water-sediment column experiments. Our findings demonstrate a unique microbiome in these urban rivers. Among the community assembly-regulating factors, both organic matter and geographic conditions play major roles in determining prokaryotic and eukaryotic community assemblies, especially regarding the critical role of organic matter in regulating taxonomic composition. Using a dissimilarity-overlap approach, we found universality in the dynamics of water and sediment community assembly in organic matter–polluted urban rivers, which is distinctively different from patterns in eutrophic and oligotrophic waters. The prokaryotic and eukaryotic communities are dominated by deterministic and stochastic processes, respectively. Interestingly, water prokaryotic communities showed a three-phase cyclic succession of the community assembly process before, during, and after organic matter pollution. Our study provides the first large-scale and comprehensive insight into the prokaryotic and eukaryotic community assembly in organic matter–polluted urban rivers and supports their future sustainable management.     

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts,U.S.A.) kettle ponds

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO₄-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.     

Restoration of lost aquatic plant communities: New habitats forChara

In the Netherlands peat was excavated for fuel until 1950. This gave rise to waterbodies (called turf ponds) which were then colonized by aquatic plants. Succession resulted in different aquatic plant communities and more terrestrialized stages such as floating fens. Nature conservation authorities started to excavate new turf ponds in 1990(ca. 2 ha y^–1) with the aim to restore calcareous, mesotraphent ecosystems by totally setting back succession. A sequence of new species was revealed by mapping the aquatic vegetation from 1990 onwards.Chara spp. proved early colonizers, which was not expected because they have not been present in ditches and ponds in the area for the last 20 years. The denseChara vegetation prevents the resuspension of organic soil and contributes to keep the water column nutrient-poor and clear. ability of species such asStratiotes aloides to colonise the ponds from adjacent waterbodies is not possible because no open contact exists between a turf pond and a ditch. Management measures, such as re-introduction, have to be considered if the full-range of aquatic plant communities remains the goal.     

Effects of stormwater sewer discharges on the aquatic community in urban canals in Lelystad

In urban areas with a separate sewerage system, the stormwater runoff is discharged into surface waters. A study on the effects of stormwater sewer discharges on the composition of the aquatic community in urban waters was carried out in two areas with a primarily residential use in the new town of Lelystad. The aquatic organisms considered included hydrophytes, epiphytic diatoms, filamentous algae and macroinvertebrates.The results indicate that the stormwater sewer discharges cause a slight change in the composition of the aquatic community. The water in the urban surface waters can be characterized as eutrophic and - toa-mesosaprobic. Near stormwater sewer outfalls the water tends to the more polluteda-mesosaprobic state. The shifts in the composition of the aquatic community could be traced primarily on the basis of a number of epiphytic diatoms and macroinvertebrates (in particular some Diptera and Trichoptera). Most hydrophytes, filamentous algae and the remaining epiphytic diatoms and macroinvertebrates (in particular water beetles and water mites) turned out to be of little or no use in this respect.Because the investigation was carried out in an unusually dry summer, the results probably underestimate the effects of stormwater discharges on the aquatic community.     

The feeding activity of Colossoma macropomum larvae (tambaqui) in fishponds with water hyacinth (Eichhornia crassipes) fertilizer.

Analysis of macrophyte water hyacinth (Eichhornia crassipes) as an organic fertilizer of Colossoma macropomum (tambaqui) larvae in ponds is provided. Water hyacinth produce an organic fertilizer at the ratio of 100 g x m(-2) in tambaqui ponds. Two groups of 5,000 larvae were transferred to two fishponds with and without water hyacinth fertilizer and reared until day 43. The fertilized pond evidenced more plankton abundance during the entire production period when compared with the control pond (P < 0.001). The phytoplankton community in the pond was not significantly different than in gut contents (P > 0.05) in both ponds (with and without organic fertilizer). Fish larvae failed to show any preference or selectivity in relation to the different algae (P > 0.01) in the pond, but exhibited high ingestion selectivity for zooplankton (P < 0.05). Application of fertilizer increased (P < 0.05) the abundance of phytoplankton and zooplankton in the treatment pond. Since water hyacinth fertilizer is quite cheap and easily available, it may be conveniently used to enhance fish yield in ponds.     

The role of pollutant accumulation in determining the use of stormwater ponds by amphibians

Urbanization often results in the creation of habitats such as stormwater management ponds. Although stormwater ponds are designed to retain runoff and associated pollutants, they are frequently colonized by wildlife including pond-breeding amphibians. Understanding of the ecological function of these created habitats is limited. This study investigated the role of pollutants in shaping use of stormwater ponds by amphibians. A survey of 68 stormwater ponds in Baltimore County, Maryland, and statistical modeling found wood frogs (Rana [= Lithobates] sylvatica) were more likely to breed in ponds with longer hydroperiods and Cl^? concentrations below approximately 250 mg/L. American toad (Bufo [= Anaxyrus] americanus) use of ponds was primarily influenced by hydroperiod; toads were more likely to use longer hydroperiod ponds. To confirm use was a result of toxicity and differential sensitivity among species, wood frog and American toad embryos and larvae were exposed to sediment from six stormwater ponds spanning the range of pollutant conditions documented in the field. Survival of wood frogs through metamorphosis was related to metal and salt levels of pond sediments, but survival of American toads was not. In agreement with the field study, no wood frog larvae survived to metamorphosis when Cl^? levels were above 260 mg/L. The results suggest that pollutants that accumulate in stormwater ponds, specifically road deicing salts, are acting as local filters capable of creating unique assemblages of anuran larvae in urban areas.     

Significant Arsenic Reduction by Pond Sediment Microflora in the Arsenic-Affected Bengal Delta

Biogeochemical reduction and mobilization of sediment-bound arsenic have triggered widespread groundwater arsenic contamination and public health emergency in Bengal Delta. The present study examines arsenic reduction ability of pond sediment microbiota and their diversity from arsenic-affected villages. Arsenic reduction ability of pond sediment microbiota and individual bacterial isolates were studied in sediment microcosm and in culture medium. Arsenic-reducing strains were identified from 16S rDNA sequences. Pond sediment microflora caused profuse arsenic reduction under anoxic and partial anoxic conditions, and under the influence of labile organic matter. Prominent arsenic-reducing strains were identified as Chryseobacterium sp., Pseudomonas sp., Acinetobacter sp., and Comamonas aquatica. The presence of partial-to-true anoxic conditions, typical of pond ecosystems in this region and labile organic matter, as well as organic manure applications in ponds for aquaculture, strongly favored arsenic reduction by sediment microflora. The Bengal Delta plain is bestowed with thousands of aquaculture ponds and floodplain wetlands which might act as important sites for microbial reduction and mobilization of arsenic to the groundwater hydrologic system in the region.     

重庆丘陵山区池塘沉积物有机碳埋藏速率及其影响因素

池塘等小型水体在全球碳循环中发挥着重要作用,是碳排放的热区,但是对池塘碳埋藏速率认识相对匮乏,限制了全面认识池塘在流域碳传输中的功能。为探究池塘沉积物有机碳埋藏速率及其影响因素,选取重庆市北碚区柳荫镇的11个池塘为研究对象,于2022年7月对池塘沉积物进行采样,分析了池塘沉积物基本理化性质,估算出池塘沉积物有机碳埋藏量和埋藏速率,并分析了池塘因素和流域因素对池塘沉积物有机碳埋藏速率的影响。结果显示：(1)沉积物总有机碳(TOC, Total Organic Carbon)含量在1.03%—3.51%之间变化,总体呈现随深度增加而逐渐降低的趋势;(2)有机碳埋藏速率均值为194.60 g m^-2 a^-1,范围区间为142.76—293.32 g m^-2 a^-1,略高于其他池塘的类似研究结果;(3)沉积物TOC含量与总氮(TN, Total Nitrogen)含量呈显著正相关(P<0.01),与流域中林地面积占比呈显著正相关(P<0.05),与旱地面积占比呈显著负相关(P<0.05),...     

The Effects of Periphyton, Fish and Fertilizer Dose on Biological Processes Affecting Water Quality in Earthen Fish Ponds

The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.