Suspended Solids Flux Research Articles

Winter atmospheric deposition of trace elements in the Arkhangelsk region (NW Russia): Insights into environmental effects

Atmospheric precipitation is an important indicator of ecological status. Snow cover accumulates all atmospheric precipitation that occurs during the cold season and releases large amounts of matter into surface water streams during spring snowmelt. We measured chemical composition of suspended solids (>0.45 μm) and dissolved matter (<0.45 μm) of atmospheric precipitation sampled on a monthly basis in 4 stations of Arkhangelsk region in cold seasons of 2018–2021. The fluxes of insoluble particles increase consistently in the spring months. In winter, the largest fluxes of suspended solids from the atmosphere were observed in the urbanized areas (in Severodvinsk and Onega). Snow in Onega showed a significant enrichment in Mn as well as Rb, Sr, Cs, Ba and Pb, which is related to boiler house emissions. Severodvinsk snow is enriched in V, Ni in dissolved fraction and Al, V, Cu, Sr, Pb in suspended solids. The environmental risk assessment shows that Onega station is affected to high and extremely polluted conditions for Mn concentration and Severodvinsk station is affected to multi-element pollution from moderate to significant levels. Comparison with the composition of the river runoff of the Northern Dvina showed that the concentrations of Cu, Zn, Cd and Pb in the snow are equal to or even higher than the river concentrations, indicating that atmospheric precipitation accumulated during winter can significantly affect the geochemistry of river runoff with respect to these elements.

A modified wash-off function for stormwater suspended solids modelling

In urban areas, the classical exponential wash-off equation for modelling of stormwater suspended solids (SS) relates the washoff of solids to the overland flow rate, assuming that runoff is proportional to rainfall. However, in catchments where infiltration occurs through the pavement surface, this assumption may not be valid. Furthermore, many researchers have concluded that the effect of rain impaction, related to rain intensity, should be considered as a separate model parameter to runoff rate. To address this problem, a semi-deterministic stormwater quality model was developed which incorporated rain intensity directly in the exponential wash-off equation. The modified function was compared to the more classical wash-off equation using a dataset of 18 storm events sampled from a separate pipe and gully system in Dublin, Ireland. The modified wash-off equation showed a consistent improvement in the fit of observed SS fluxes at the outlet of the drainage system: the Nash-Sutcliffe index of modelled performance increased from 0.39 to 0.58 on average using the modified wash-off function. The form of the modified wash-off function allows for simple integration into many stormwater quality models currently in use, without the need for any additional model parameters.

Joint Sensing of Bedload Flux and Water Depth by Seismic Data Inversion

AbstractRivers are the fluvial conveyor belts routing sediment across the landscape. While there are proper techniques for continuous estimates of the flux of suspended solids, constraining bedload flux is much more challenging, typically involving extensive measurement infrastructure or labor‐intensive manual measurements. Seismometers are potentially valuable alternatives to in‐stream devices, delivering continuous data with high temporal resolution on the average behavior of a reach. Two models exist to predict the seismic spectra generated by river turbulence and bedload flux. However, these models require estimating a large number of parameters and the spectra usually overlap significantly, which hinders straightforward inversion. We provide three functions contained in the R package “eseis” that allow generic modeling of hydraulic and bedload transport dynamics from seismic data using these models. The underlying Monte Carlo approach creates lookup tables of potential spectra, which are compared against the empirical spectra to identify the best fitting solutions. The method is validated against synthetic data sets and independently measured metrics from the Nahal Eshtemoa, Israel, a flash flood‐dominated ephemeral gravel bed river. Our approach reproduces the synthetic time series with average absolute deviations of 0.01–0.04 m (water depth, ranging between 0 and 1 m) and 0.00–0.04 kg/sm (bedload flux, ranging between 0 and 4 kg/sm). The example flash flood water depths and bedload fluxes are reproduced with respective average deviations of 0.10 m and 0.02 kg/sm. Our approach thus provides generic, testable, and reproducible routines for a quantitative description of key metrics, hard to collect by other techniques in a continuous and representative manner.

The influence of dam construction on water quality in the lower Geum River, Korea

AbstractThe Geum River has been faced with extreme environmental change due to the construction of three dams in midstream since 2012 (Four Major River Restoration Project). We hypothesized that suspended solids (SS) and total particulate phosphorus (TPP) decreased after the dam construction. To test our hypothesis, we investigated the influence of the dam construction on water quality by measuring possible impacts of decreasing SS, total phosphorus (TP), and TPP on the ecosystem in the lower Geum River and the Geum River estuary. For this study, we chose one site to compare the monthly water quality data pre‐construction (2008) and post‐construction (2015). Dissolved oxygen and pH were not significantly different between pre‐ and post‐construction, while electric conductivity (EC) increased. The increase in the EC may be related to a decrease in river discharge (RD) after the dam construction. As we expected, TP and TPP decreased post‐construction, but SS did not show significant differences between pre‐ and post‐construction. This suggests that the decline of TPP concentrations post‐construction were not related to SS levels. The explosive algal bloom and sedimentation of the algae may be an important factor in explaining the decrease in TP and TPP. The decline of SS, TP, and TPP flux to the lower Geum River was observed. This could be a potential reason for the erosion of the mud flat of the Geum River estuary in the future. Therefore, to determine the long‐term effects of the SS and the phosphorus fluxes to the lower Geum River, these factors should be monitored periodically over longer periods of time than this study.

Negligible contribution of reservoir dams to organic and inorganic transport in the lower Mimi River, Japan

Rivers fulfill an essential ecological role by forming networks for material transport from upland forests to coastal areas. The way in which dams affect the organic and inorganic cycles in such systems is not well understood. Herein, we investigated the longitudinal profiles of the various components of the water chemistry across three cascade dams in Japan: the Yamasubaru Dam, Saigou Dam, and Ohuchibaru Dam, which are situated along the sediment-productive Mimi River in different flow conditions. We analyzed the following water quality components: suspended solids (SS), turbidity, total iron (TFe), dissolved iron (DFe), total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), humic substance (HS), and major ionic components (Na+, Mg2+, Ca2+, Cl−, NO3−, and SO42−) in the downstream channels of the three dams during the low–intermediate-flow and high-flow events from 2012 to 2014. We estimated hourly loads of each component using hourly turbidity data and discharge data (i.e., L–Q model) separately, and the results are integrated to estimate the annual fluxes. The annual fluxes between the methods were compared to verify predictability of the conventional L–Q models. Annual flux of TOC, TN, DFe, and HS estimated by the turbidity displayed similar values, whereas the flux of SS, TFe, and TP tended to increase downstream of the dams. Among the dams, estimated flux proportions for TP and TFe were higher during high-flow events (74%–94%). Considering geographic conditions (e.g., absence of major tributary between the dams), the result implies that accumulated TP and TFe in the reservoirs may be flushed and transported downstream with SS over the short height dams during flood events. Assuming this process, the reservoir dams probably make only a fractional contribution to the organic and inorganic transport in the catchment studied. The percent flux errors for SS, TFe, and TP fluxes ranged from −7.2% to −97% (except for the TP flux in 2013), which highlights the risk of underestimating these components when using an L–Q model.

Impact of land uses on heavy metal distribution in the Selenga River system in Mongolia

The Selenga River contributes to 50% of the total inflow to Lake Baikal. Large tracts of the Selenga River Basin have been developed for industry, urbanization, mining, and agriculture, resulting in the release of suspended solids (SS) that affect downstream water quality and primary productivity. This study addressed SS as the main factor controlling pollutant transport and the primary indicator of land degradation in the Selenga River system. Tributaries with larger areas dedicated to agricultural use had higher SS concentrations, reaching 862 mg L−1, especially during the high runoff and intensive cultivation season. Although the large SS flux was detected in the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to widespread development in the watershed. Watersheds with high potential of SS release are sensitive to intensive land uses. SS in the river system had a constant elemental composition consisting mainly of Fe and Al oxides, indicating that surface soils were major constituents of the tributary SS. Three minor heavy metals (Zn, Cu, and Cr) appeared in high concentrations downstream of urban and mining areas (two- to sixfold increases), indicating that these contaminants are carried by SS. At two tributary junctions, the concentration of contaminants on the SS decreased due to a large influx of SS with low heavy metal contents. Changes in electric conductivity and pH at downstream of tributary junctions enhanced the sedimentation of SS and the removal of contaminants from the water phase after aggregation of the SS. Land use changes in the tributary watersheds are major controlling factors for the fate of contaminants in the river system.

Using the mineralogy of river sediments as pollution indicator of clay mining activity

ABSTRACT View of the difficulty to elect standards for water pollution control in clay mining activity, this study aimed to verify the possibility of using the mineralogy of river sediments as a pollution indicator of clay mining activity. The study was carried out in the Assistência Stream basin, located in the largest ceramic pole of the Americas. Surface water samples of Assistência Stream were collected in 67 field campaigns in 2014. This stream showed an average annual discharge of 0.8 m3.s-1 with an annual flux of suspended solids of 3,680 t.year-1 and an annual flux of dissolved solids of 4,234 t.year-1. The mineralogical analysis of fluvial sediments indicated the presence of quartz, montmorillonite, illite and kaolinite in the fraction &lt;53 micrometers. The kaolinite is from the surface soil erosion. However, the illite, predominant clay mineral in the rocks explored by mining, is practically absent in the surface horizon of the Assistência Stream basin. Thus, its presence in the suspended solids transported by Assistência Stream is associated with atmospheric deposition of dust produced during clay mining activities present in this watershed.

Quantifying nutrient and suspended solids fluxes in a constructed tidal marsh following rainfall: The value of capturing the rapid changes in flow and concentrations

Coastal tidal wetlands are perceived to provide nutrient dissipation services and serve as the final buffer between excess nutrient loads coming from nearby upland watersheds and sensitive estuarine waters. The construction and restoration of tidal marshes has the potential to benefit coastal waters. However, the water quality services of tidal wetlands have yet to be established with any certainty. This is in part due to the difficulty of monitoring these systems where flow and concentrations vary widely with tidal ebb and flood along with rainfall events mobilizing nutrients in pulses from upstream watersheds. In this article, we show over a period of 10 days following a rainfall event, the value of high temporal resolution data to characterize the complex nutrient and flow dynamics and to reliably calculate material balances in a created coastal marsh in North Carolina. Ultraviolet–visible spectrometers were used to obtain 15-min concentration data for nitrate, total Kjeldahl nitrogen, dissolved organic carbon, total suspended solids, phosphate, and total phosphorus. Our results show that a pulse of nitrate moved through the marsh from upstream agricultural production following the rainfall event and 25% (13kg of 53kg) of the nitrate was retained in the marsh over a period of 10 days. No other material showed a clear pulse from the upstream agricultural production. The marsh acted as a sink for total suspended solids (40kg) and had near neutral mass balances for dissolved organic carbon, total Kjeldahl nitrogen, total phosphorus, and phosphate. Subsequent simulations indicated that different and erroneous results would have been obtained from 2-, 6- or 12-h sampling intervals. These results demonstrate, even on a short term basis, why high-frequency data acquisition is necessary in these tidal marsh systems to truly quantify their impact on water quality ecosystem services.

A sensor network for high frequency estimation of water quality constituent fluxes using surrogates

Characterizing spatial and temporal variability in the fluxes and stores of water and water borne constituents is important in understanding the mechanisms and flow paths that carry constituents to a stream and through a watershed. High frequency data collected at multiple sites can be used to more effectively quantify spatial and temporal variability in water quality constituent fluxes than through the use of low frequency water quality grab sampling. However, for many constituents (e.g., sediment and phosphorus) in-situ sensor technology does not currently exist for making high frequency measurements of constituent concentrations. In this paper we describe how water quality measures such as turbidity or specific conductance, which can be measured in-situ with high frequency, can be used as surrogates for other water quality constituents that cannot economically be measured with high frequency to provide continuous time series of water quality constituent concentrations and fluxes. We describe the observing infrastructure required to make high frequency estimates of water quality constituent fluxes based on surrogate data at multiple sites within a sensor network supporting an environmental observatory. This includes the supporting sensor, communication, data management, and data storage and processing infrastructure. We then provide a case study implementation in the Little Bear River watershed of northern Utah, USA, where a wireless sensor network has been developed for estimating total phosphorus and total suspended solids fluxes using turbidity as a surrogate.

The freshwater tidal wetland Liberty Island, CA was both a source and sink of inorganic and organic material to the San Francisco Estuary

It is hypothesized that perennial freshwater tidal wetland habitat exports inorganic and organic material needed to support the estuarine food web and to create favorable habitat for aquatic organisms in San Francisco Estuary. It is also hypothesized that most of the material flux in this river-dominated region is controlled by river flow. The production and export of material by Liberty Island were measured and compared using discrete monthly and continuous (15 min) measurements of a suite of inorganic and organic materials and flow between 2004 and 2005. Seasonal material flux was estimated from monthly discrete data for inorganic nutrients, suspended solids and salts, organic carbon and nitrogen and phytoplankton and zooplankton group carbon and chlorophyll a and pheophytin pigment. Estimates of material flux from monthly values were compared with measured daily material flux values for chlorophyll a concentration, salt and suspended solids obtained from continuous measurements (15 min) using YSI water quality sondes. Phytoplankton carbon produced within the wetland was estimated by in situ primary productivity. Most inorganic and organic materials were exported from the wetland on an annual basis, but the magnitude and direction varied seasonally. Dissolved inorganic nutrients such as nitrate, soluble phosphorus, total phosphorus and silica as well as total suspended solids were exported in the summer while total and dissolved organic carbon were exported in the winter. Salts like chloride and bromide were exported in the fall. Chlorophyll a and pheophytin were exported in the fall and associated with diatom and cyanobacteria carbon. Mesozooplankton carbon was dominated by calanoid copepods and exported most of the year except summer. Continuous sampling revealed high hourly and daily variation in chlorophyll a, salt and total suspended solids flux due to high frequency changes in concentration and tidal flow. In fact, tidal flow rather than river discharge was responsible for 90% or more of the material flux of the wetland. These studies indicate that freshwater tidal wetlands can be a source of inorganic and organic material but the export of material is highly variable spatially and temporally, varies most closely with tidal flow and requires high frequency measurements of both tidal flow and material concentration for accurate estimates.

Resuspension of Mercury-Contaminated Sediments from an In-Lake Industrial Waste Deposit

The resuspension and transport of particulate mercury HgP from a nearshore industrial waste deposit to the pelagic zone of Onondaga Lake, N.Y., was investigated using an array of sediment traps radiating from the deposit, and quantified through application of a steady-state mass balance model. Time-averaged downward fluxes of suspended solids and HgP decreased in the offshore direction, indicating a nearshore source. Strong temporal variations in resuspension were documented and were linked to the dynamics of wind- driven wave action, as quantified by a validated surface wave model. A simple steady-state model of offshore transport from the resuspension zone, which assumes a balance between offshore transport and settling, was used to analyze sediment trap data. The resulting larger, and likely more accurate, estimate of HgP resuspension 60 g day 1 represents the dominant contemporary source to the water column. This result supports the planned remediation of this source as a part of a Superfund cleanup project. DOI: 10.1061/ASCE0733-93722009135:7526 CE Database subject headings: Sediment; Mercury; Mass transport; Industrial wastes; Lakes.

Rethinking the Contribution of Drained and Undrained Grasslands to Sediment‐Related Water Quality Problems

Grass vegetation has been recommended for use in the prevention and control of soil erosion because of its dense sward characteristics and stabilizing effect on the soil. A general assumption is that grassland environments suffer from minimal soil erosion and therefore present little threat to the water quality of surface waters in terms of sediment and sorbed contaminant pollution. Our data question this assumption, reporting results from one hydrological year of observations on a field-experiment monitoring overland flow, drain flow, fluxes of suspended solids, total phosphorus (TP), and molybdate-reactive phosphorus (<0.45 mum) in response to natural rainfall events. During individual rainfall events, 1-ha grassland lysimeters yield up to 15 kg of suspended solids, with concentrations in runoff waters of up to 400 mg L(-1). These concentrations exceed the water quality standards recommended by the European Freshwater Fisheries Directive (25 mg L(-1)) and the USEPA (80 mg L(-1)) and are beyond those reported to have caused chronic effects on freshwater aquatic organisms. Furthermore, TP concentrations in runoff waters from these field lysimeters exceeded 800 mug L(-1). These concentrations are in excess of those reported to cause eutrophication problems in rivers and lakes and contravene the ecoregional nutrient criteria in all of the USA ecoregions. This paper also examines how subsurface drainage, a common agricultural practice in intensively managed grasslands, influences the hydrology and export of sediment and nutrients from grasslands. This dataset suggests that we need to rethink the conceptual understanding of grasslands as non-erosive landscapes. Failure to acknowledge this will result in the noncompliance of surface waters to water quality standards.

Floodplain hydrology in an Amazon floodplain lake (Lago Grande de Curuaí)

Summary The floodplains of the Amazon basin influence the hydrology and fluxes of suspended solids and solutes on multiple scales. Our study focused on the floodplain of Lago Grande de Curuao´ (Obidos, Brazil), a 4000 km 2 segment of floodplain and local upland catchment representative of the lower Amazon. Based on in situ and satellite data acquired from 1997 to 2003, we calculated the exchanges of water between the floodplain and the river and determined the temporal dynamics of flooded area water derived from river flooding, rainfall, runoff, and exchange with groundwater annually for six years. The Ama- zon River dominated the inputs of water to the flooded area year-round, accounting about 77% of the annual total inputs; rainfall and runoff accounted for about 9% and 10%, respec- tively, while seepage from the groundwater system accounted for 4%. The hydrologic residence time of the lake was about three months, and the floodplain made a net contri- bution of water to the river. The exported volume (net balance between water input and

On-line determination of sludge settling velocity for flux-based real-time control of secondary clarifiers

The state diagram for operation of secondary clarifiers is used to design a control algorithm for the return sludge pumping and determination of the actual hydraulic capacity of the biological step of a wastewater treatment plant. On-line input for the control algorithm is derived from a sludge volume sensor and a suspended solids sensor in the form of software sensors giving values for the sludge settling characteristics - settling velocity, sludge volume index, initial settling velocity and the exponent in the Vesilind equation - allowing the control to accommodate the ever changing settling characteristics and thereby keep the suspended solids flux in the clarifiers in balance for both dry weather flows and during rain events. The control algorithm has been implemented, tested and set into normal operation on a full scale wastewater treatment plant.

Quantifying Long-Term NPS Pollutant Flux in an Urbanizing Watershed

Long-term nonpoint source (NPS) pollutant flux is described within the rapidly developing Occoquan watershed west of Washington, D.C. Data consist of up to 24 years of observed rainfall, integrated pollutant discharge, and land use/land cover from four headwater basins of the Occoquan River. Three of the four study basins, ranging in size from 67 to 400 km2 , are predominantly forest and mixed agriculture. The fourth basin, the 127 km2 Cub Run watershed, has urbanized rapidly over the past 20 years. Higher annual NPS sediment and nutrient fluxes in Cub Run after 1983 are linked to increased soil disturbance from urban construction and increased storm volumes resulting from increased mean impervious percent. Over the long-term, storm fluxes of NPS particulate P, soluble P, particulate N, and soluble N make up 92, 67, 89, and 50%, respectively, of the total fluxes of those constituents, with between 88 and 98% of mean annual total suspended solids fluxes delivered by storm flow. Higher NPS pollutant fluxes ...

Sediment and nutrient losses from exotic Pinus plantation management operations under simulated rainfall

Summary Rainfall simulation experiments were carried out to measure runoff and soil water fluxes of suspended solids, total nitrogen, total phosphorus, dissolved organic carbon and total iron from sites in Pinus plantations on the coastal lowlands of south-eastern Queensland subjected to various operations (treatments). The operations investigated were cultivated and nil-cultivated site preparation, fertilised site preparation, clearfall harvesting and prescribed burning; these treatments were compared with an 8-y-old established plantation. Flow-weighted mean concentrations of total nitrogen and total phosphorus in surface runoff from the cultivated and nil-cultivated site-preparation, clearfall harvest, prescribed burning and 8-y-old established plantation treatments were very similar. However, both the soil water and the runoff from the fertilised site preparation treatment contained more nitrogen (N) and phosphorus (P) than the other treatments — with 3.10 mg L−1 and 4.32 mg P L− (4 and 20 times more) in the runoff. Dissolved organic carbon concentrations in runoff from the nil-cultivated site-preparation and prescribed burn treatments were elevated. Iron concentrations were highest in runoff from the nil-cultivated site-preparation and 8-y-old established plantation treatments. Concentrations of suspended solids in runoff were higher from cultivated site preparation and prescribed burn treatments, and reflect the great disturbance of surface soil at these sites. The concentrations of all analytes were highest in initial runoff from plots, and generally decreased with time. Total nitrogen (mean 7.28, range 0.11–43.27 mg L−) and total phosphorus (mean 11.60, range 0.06–83.99 mg L−) concentrations in soil water were between 2 and 10 times greater than in surface runoff, which highlights the potential for nutrient fluxes in interflow (i.e. in the soil above the water table) through the general plantation area. Implications in regard to forest management are discussed, along with results of larger catchment-scale studies.

Sedimentation, suspension, and resuspension in Tasman Bay and Beatrix Bay, New Zealand, two contrasting coastal environments which thermally stratify in summer

The influence of density stratification on sedimentation, suspension, and resuspension in Tasman Bay and Beatrix Bay, New Zealand, two contrasting coastal environments, was studied with specific reference to the implications for modelling aquaculture sustainability. Tasman Bay, an enhanced scallop (Pecten novaezelandiae Reeve) fishery, is a very large coastal indentation gently shelving to c. 20 m deep c. 10 km from shore and open to the Tasman Sea, whereas Beatrix Bay, an area of intense Greenshell™ mussel (Perna canaliculus Gmelin) aquaculture, is a small (22 km2 × 30–40 m deep) enclosed embayment off the side of the nearby Pelorus Sound. Sediment trap arrays were used to determine the vertical fluxes of suspended solids and the associated chlorophyll component. Benthic chambers were used to investigate sediment nutrient regeneration. In summer, salinity gradients in both bays are minimal or non‐existent because of low inputs of fresh water and density stratification is mainly controlled by water temperature. The data from mid summer exhibited different spatial distribution patterns for detritus and phytoplankton biomass (as indicated by chlorophyll) in these two very different bays, although they had similar turbulent environments. The density discontinuity at the thermocline had a strong influence on settling of phytoplankton. There was evidence of upwards entrainment of suspended paniculate matter into the upper water column from the thermocline in Beatrix Bay. Benthic resuspension was estimated to contribute up to 90% of the suspended solids caught in sediment traps near the sea floor in both bays. The trapping rate of phytoplankton was thought to be dependent on species dominance. Possible mechanisms of resuspension included turbulence in the benthic boundary layer, and high velocities below the thermocline associated with internal seiches. The presence of a mid water column chlorophyll maximum in Beatrix Bay is discussed in terms of nutrient and light regimes at the thermocline, and species composition. In Tasman Bay, the chlorophyll maximum was thought to be caused by resuspension of benthic microphytes and their subsequent confinement in a thin layer (2–4 m thick) of high turbulence between the thermocline and the seabed.

Suspended sediment in the Rivers Tweed and Teviot

Suspended solids concentrations were monitored over a 3-year period from April 1994 to March 1997 at two sites on the River Tweed and one on the Teviot, a tributary of the Tweed. Values of the median suspended solids concentration ranged between 6.6 and 8.0 mg l −1 for the three sites. The relationship between suspended solids concentration and flow varied both between years and by month, showing the influence of sediment supply and diatom growth. Estimates of the flux of suspended solids from the Tweed basin at the tidal limit ranged from 38 000 to 89 800 t year −1, depending on the year. Converted into a yield, these values are at the lower end of the range of both published estimates and those for other LOIS rivers.

Suspended Solids Flux Between Salt Marsh and Adjacent Bay: A Long-term Continuous Measurement

The beneficial roles of coastal salt marshes have been well identified as a storm surge protector, a nursery for young fish and a natural filter for pollutants. However, the vectors of nutrients and suspended solids exchanges between the salt marsh and the adjacent bay are not completely known. In this study, suspended solids flux between a salt marsh at Tuckerton, New Jersey, U.S.A. and Great Bay was continuously measured for an extended period of time by an improved monitoring methodology. A field infrared nephelometric turbidimeter was deployed to measure turbidity continuously at the mouth of the tidal creek, and the measured turbidity data were used to derive suspended solids concentrations. Current velocity and water surface elevation were measured concurrently at the same location. During the monitoring period from March to October 1996, suspended solids were found to be imported into the salt marsh from the adjacent bay. The small net import appeared to be inadequate for wetlands areal viability when compared to the relative sea-level rise rates. Results of this study suggested that a minimum of five water sample sets were needed to establish a reasonably good overall TSS-turbidity regression relationship in terms of flux quantification.

Fluxes and mass balances of nutrients in a semi-intensive shrimp farm in north-western Mexico

Fluxes of suspended solids, chlorophyll a and nutrients (phosphorus, nitrate, nitrite and ammonia) were estimated in a semi-intensive shrimp farm in north-west Mexico for two consecutive cycles of production encompassing both the dry and wet seasons. A mass balance model was developed for nitrogen and phosphorus and fluxes estimated included shrimp feed, fertilization, shrimp stocked, harvest, macrofauna associated, water exchange, filling and drainage. Of the total nitrogen and phosphorus input to the ponds, 35.5% and 6.1% were recovered in 1822 kg ha−1 of shrimp harvested. Volatilization of ammonia and adsorption by sediments of phosphorus constituted 27.4% and 63.5%, respectively; the estimated environmental losses of nitrogen and phosphorus per t of shrimp produced were 28.6 kg and 4.6 kg, respectively. Assuming that all the shrimp farms in Sinaloa (Mexico), operate according to the model, the farms could represent a load corresponding to the untreated sewage generated by 56 200-192 750 and 43 500-149 170 people in terms of nitrogen and phosphorus discharged annually.