Seasonal Changes in Water Quality in Commercial Channel Catfish Ponds in Mississippi

Selected water quality variables were measured at monthly intervals for 1 yr in 10 commercial channel catfish ponds in northwest Mississippi. Temporal changes in most variables appeared to be related to seasonal periodicity of phytoplankton abundance. Phytoplankton standing crops and total organic matter were highest in summer months when primary production was favored by warm water temperatures, high solar irradiance, and large inputs of nutrients resulting from high summer fish feed allowances. As day length, water temperature, and feed inputs decreased in autumn and winter, phytoplankton abundance and organic matter concentrations decreased. Seasonal changes in total nitrogen and total phosphorus concentrations were similar to phytoplankton abundance because much of the total nitrogen and phosphorus was contained within phytoplankton cells. Contrasting to the seasonal trend for total nitrogen, concentrations of dissolved inorganic nitrogen were lowest in the summer and highest in the cooler months. Rapid assimilation by phytoplankton served to maintain relatively low concentrations of dissolved inorganic nitrogen during the summer despite highest nitrogen loading rates during that period. Low water temperatures and generally less favorable conditions for phytoplankton growth decreased rates of nitrogen assimilation in the winter and ammonia, nitrite, and nitrate accumulated. Soluble reactive phosphorus concentrations were low throughout the year because physico-chemical processes, such as precipitation and adsorption to bottom muds acted to continually remove inorganic phosphorus from the water column.     

枸杞岛贻贝养殖水域碳氮磷分布格局

于2013年贻贝成熟期和幼苗期对枸杞岛贻贝筏式养殖水域营养分布和碳分布格局开展相关实验。结果表明:从生态健康角度,夏季成熟期的贻贝养殖造成养殖海域氮、磷营养盐浓度升高,尤其是无机氮浓度显著高于非养殖区(P<0.05),养殖区处于受磷限制性的重富营养化,对其水体健康产生一定压力;秋季幼苗期贻贝养殖使养殖海域氮、磷浓度均降低,尤其是无机氮浓度显著低于非养殖区(P<0.05),与夏季分布格局相反,对水体有净化作用。从生态效应看,贻贝养殖使表层水体中溶解无机碳浓度显著低于非养殖区(P<0.05),产生碳汇效应;同时,贻贝养殖使水体中溶解有机碳浓度显著高于非养殖区(P<0.05),由于丰富的氮营养盐,溶解有机碳处于不稳定态,为碳源。因此,成熟期与幼苗期贻贝养殖对其水域健康产生不同作用,养殖的碳汇、碳源还有待进一步的系统研究。     

Benthic Recovery after the Cessation of a Gilt‐head Seabream,Sparus aurata,Farm in the Mediterranean Sea

An environmental recovery study was carried out after the cessation of a gilt‐head seabream farm off the Mediterranean coast of Spain. Physicochemical variables of sediments, in situ benthic fluxes of oxygen and nutrients, and benthic macrofauna were measured in the farming area and at a control station. Five sampling campaigns were done, one before the closure and the others at 1, 3, 9, and 24 mo after cessation. Benthic flux of ammonium was the first variable to recover, followed by benthic fluxes of phosphate and dissolved oxygen and percentage organic matter in the sediments, which 3 mo after the cessation of farming already showed levels similar to those in the control station. Nine months after cessation, the other abiotic variables of the sediments disturbed by the activity had recovered, such as percentage coarse fraction, total phosphorus concentrations, and redox potential measurements. The recovery of the macrofauna was slower than the abiotic variables. Three months after cessation, Capitella capitata abundance had reduced drastically in the farming area, but similar specific richness levels were not observed between the two sampled zones until 2 yr after farming cessation.     

Effects of marine fish farming on nutrient composition and plankton communities in the Eastern Aegean Sea (Turkey)

The hypothesis that the presence of fish farming zones affects the water quality and plankton communities was investigated in an Aegean Sea fish farm during February, June, September and January 2000–2001. In the spatial coverage, a total of 12 stations were sampled; three of them were reference stations. A variance analysis was applied to the measurements made at the stations near the fish farms and at the control stations. While no significant differences in concentrations of nutrients, chlorophyll a, particulate organic carbon and particulate organic nitrogen were detected between the stations and the control sites within one season, significant differences were detected between the parameter values measured except for total dissolved phosphorus and dissolved organic phosphorus at different seasons. The seasonal differences were also significant with regard to the biodiversity. Together with these temporal differences in general, there was a higher diversity of species at the control site as compared with the other stations in September, which was the key season to detection of significant changes. The most important consideration is that it is not sufficient to take the instantaneous values for the physico‐chemical variables; rather, it is necessary to monitor the biological parameters in order to define the differences in the ecosystem.     

Loading of nutrient from a land-based fish farm(Orbetello, Italy) at different times

. A marine fish farm (production ~ 100 tonnes per year) located in the Orbetello lagoon area (Tuscany, Italy) was selected to study the waste water quality discharged. The aims of study were: a) quantify the nitrogen and phosphorus discharged from the fish farm at the beginning and the end of feeding time; b) verify nutrient trend during a daily cycle, and difference of release between nitrogen and phosphorus by reared biomass. From June 1999 to May 2000, water temperature, pH, salinity, dissolved oxygen and redox were hourly recorded in output wastewater station (E). Two water sampling strategies were adopted: monthly and daily. Monthly, in E, two field water samples at 8:00 a.m. (E8), at the beginning of feeding, and at 4:00 p.m. (E16), at the end of feeding, were collected. The dissolved and particulate nitrogen and phosphorus were analysed. With respect to total dissolved nitrogen (TDN), the total ammonia (NH₃ + NH₄⁺) concentration constituted more than 64%. With respect to total nitrogen and phosphorus, the particulated component represented, respectively, the 16% and 29–36%. A 24 h water sampling, at 4:00, 10:00, 12:00 a.m and at 4:00, 8:00, 12:00 p.m., was carried out. The results showed that TDN was excreted shortly after feeding, with a peak 4 h after the end of feeding. Most of the total dissolved phosphorus (TDP) was excreted after many hours, with a peak 8 h after the end of feeding.     

Heavy metal concentrations and sediment quality of a cage farm on Lake Volta,Ghana

This study involved the determination of sediment quality and heavy metals in the water column and bottom sediment of a selected cage fish farm in Lake Volta, to assess the potential impact of metals and organic matter pollution on the lake due to cage fish farming. Sediment analysis indicated that the texture of all sampling sites was sandy clay loam with sand dominating with a range of 31.5%–81.2%. The organic matter (TOM) ranged from 4.42%–8.89%, while organic carbon (TOC) was from 2.57%–5.22%. Total nitrogen (TN) fluctuated between 0.22% and 0.45%; total phosphate ranged between 0.22% and 5.30%. The TOC, TOM and TN content in the farm sediment were significantly lower than those of the reference sites (ANOVA, p < .05). Lead, copper, cadmium and selenium were not detected in the water. The results revealed that heavy metal concentrations in the water column and sediments were low and within tolerable levels, indicating no influence of metals from fish feed was observed on the lake water quality. However, the farm seemed to have moderate impact on sediment quality from organic matter. Water and sediment quality monitoring should be embarked upon periodically to ensure sustainable cage culture in the Lake Volta.     

Effect of organic nitrogen and carbon mineralization on sediment organic matter accumulation in fish ponds

In aquaculture, ponds with high loads of organic inputs, organic matter accumulates at the bottom over time. Uneaten feed, senescent phytoplankton and faeces are the principal sources of accumulated material, but quantifications are scarce. The sedimented organic matter develops into a flocculent layer in which different processes transform the material into inorganic forms. A better understanding of factors influencing organic matter accumulation/decomposition in the sediment is needed to better understand and manage the dynamics of nitrogen in fish ponds. In this study, the rate of mineralization of organic nitrogen and the nitrogen flux between the sediment and the water column were measured. Organic matter accumulation in fish ponds was quantified, and the data were used to construct, calibrate and validate a dynamic simulation model of organic matter deposition/decomposition in fish ponds. The accumulating material consisted of dead phytoplankton, fish faeces and uneaten feed. Through model calibration, the proportion of these materials in the total accumulated organic matter was determined. In the model, gross photosynthetic rate was estimated from an empirical relationship with feed input. After calibration, the model was validated using independent data. The model simulated well the concentrations of organic carbon and nitrogen in the sediments but it may be developed further, especially by considering the effects of resuspension.     

Comparative changes in water quality and role of pond soil after application of different levels of organic and inorganic inputs

Changes in water parameters were studied in a yard experiment for 7 weeks after application of cow dung at 20, 50 and 100 t ha^?1, poultry manure at 4, 10 and 20 t ha^?1, feed mixture (groundnut oil cake and rice bran at 1:1) at 10, 20 and 30 t ha^?1 and inorganic fertilizers at 100 kg urea+50 kg single super phosphate (SSP) ha^?1, twice this dose (2x ha^?1) and thrice this dose (3x ha^?1). To study the role of soil in the mineralization process, each treatment was divided into two groups – one with and the other without soil substrate. Higher degree of changes in water parameters was observed at higher input levels. Both organic amendment and inorganic fertilization caused significant reduction (P<0.05) in dissolved oxygen and increase in free CO₂, dissolved organic matter, total ammonia, nitrite, nitrate and phosphorus contents of water. Organic inputs significantly decreased (P<0.05) water pH and increased total alkalinity and hardness. In contrast, inorganic fertilization caused a significant increase in pH; alkalinity and hardness increased significantly in the presence of soil, but reduced in its absence. In organic input, presence of soil substrate caused significantly lower value of pH, dissolved oxygen, dissolved organic matter and phosphate‐phosphorus and significantly higher free CO₂, alkalinity, hardness, ammonia, nitrite and nitrate contents, compared with those in the absence of soil, revealing enhanced microbial mineralization in the presence of soil.     

Effects of organic effluents from a salmon farm on a fjord system. I. Vertical export and dispersal processes

Vertical flux of organic waste from a Norwegian salmon farm (which produced 2910 tonnes of fish in 19 months) located in 230-m-deep water was measured nine times in the course of 2 years by sediment traps along a transect stretching from the farm and 3 km out towards the sea. The chemical composition of the trapped material and the sediment below the traps were analyzed. The results showed that when the fish farm was empty, sedimentation rates of organic matter were similar all along the transect. Throughout the production cycle high and very variable sedimentation rates of particulate organic matter, particulate organic carbon and particulate organic nitrogen were measured within 250 m from the farm, while between 550 and 3000 m away from the farm sedimentation rates were lower and constant throughout the cycle. During the second year of production, the annual vertical flux of particulate organic carbon to the bottom adjacent to the farm was 365 g m^− 2, nine times as high as what was found 3 km away from the farm. While the sedimentation rates showed that most of the waste matter settled within 250 m of the farm, the fatty acid composition and δ¹³C isotope ratio of the material in the bottom traps indicate that some components of the organic waste were transported as far as 550 to 900 m, probably due to resuspension of surface sediment. Despite the high sedimentation rates the content of sedimentary organic matter, total organic carbon and total organic nitrogen was not elevated in the sediment around the farm. However, phosphorus was found in higher concentrations in the sediments close to the farm, indicating that organic matter had settled on the sediment and been decomposed. The unchanged content of organic matter in the sediment during the production cycle showed that at this site the local resuspension and dispersal conditions and the decomposition capacity of the benthos were sufficient to prevent overloading of the locality.     

大鹏澳海湾养殖生态环境的化学计量分析

根据2008 2009年在深圳大鹏澳养殖海域周年4个季节的生态环境调查数据,采用化学计量学方法(主成分分析、系统聚类分析和分类主成分分析)研究了大鹏澳养殖海域生态环境的时空变化。结果表明,第一主成分以海水温度、盐度、海水营养盐中的无机三氮、硫化物、叶绿素a(Chla)和颗粒有机物(POM)等为特征,表征了大鹏澳海洋生态环境主要受气候和水文因素的影响;第二主成分以海水磷酸盐(PO4-P)和沉积物硫化物为特征,与网箱养殖自身污染效应有关;第三主成分以海水溶解氧(DO)和化学需氧量(CODMn)为特征,与养殖生物耗氧代谢活动有关;第四主成分以沉积物有机质为特征,与养殖贝类的生物沉降作用有关。该养殖海域生态环境的时空分布特征主要受亚热带季风气候和养殖活动的空间布局及其季节周期性养殖生产的共同影响。