Processes Affecting Water Quality Research Articles

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.

Heterogeneities in ground-water geochemistry in a sand aquifer beneath an irrigated field

The contamination of shallow aquifers by elevated nitrate concentrations is a common problem in many rural regions of the world. Aquifers under irrigated land are especially susceptible to this type of contamination. An intensive three-dimensional investigation of water chemistry was undertaken in a shallow unconfined sand aquifer in an area of intensive irrigation in Mason County, Illinois, in order to investigate processes affecting water quality. Results reveal considerable heterogeneity in the aqueous chemistry in three spatial dimensions and temporally. Recharge is rapid in this system and the water chemistry of the recharge water is variable both spatially and temporally, being especially influenced by agricultural practices. Nitrate concentrations are elevated in a zone between about 6 and 10 m beneath the surface, although in certain areas and at certain times this zone was not found. The maximum nitrate concentrations in this zone were slightly greater than 20 mg l −1 as N, well above the US Environmental Protection Agency's maximum contaminant level (MCL) of 10 mg l −1. Nitrate was generally absent both above and below this depth in the aquifer. Water relatively depleted in nitrate recharges the aquifer from the surface at the site, producing a zone of dilute water near the water table. Beneath the plume, denitrification reactions are responsible for removing nitrate from solution, probably mainly coupled to oxidation of sulfide minerals; tritium data suggest that vertical movement of solutes is rapid and thus there has been enough time to transport surface-applied fertilizer to depths in excess of 30 m in the aquifer. This rapid vertical movement is almost certainly enhanced by intensive irrigation in the county. A number of aqueous species and chemical parameters (Ca, Mg, Sr, Fe, Si, dissolved inorganic carbon (DIC), dissolved oxygen, total dissolved solids, and pH) are correlated with nitrate concentrations, primarily because, like nitrate, they are either a significant fraction of fertilizers or are redox-sensitive. Drinking water quality is generally not degraded by fertilizer applications in this area, because almost all drinking-water wells are screened well below the zone of elevated nitrate concentrations.

A Multi-disciplinary Study of Frontal Systems in the Tay Estuary, Scotland

The results of a remote sensing study of tidal mixing processes in the Tay Estuary have been correlated with the results of mathematical and physical models and ground sampling data in an attempt to assess the nature, the spatial and temporal extent and the variability in the formation of convergent fronts in the Tay Estuary. The application of remote sensing methods to the study of estuarine mixing processes in the Tay Estuary, supported by ground measurements, has discovered convergent front mechanisms and complex hydrodynamic processes which had not previously been recognized in the Tay Estuary. This integrated approach has enabled the various features and mixing mechanisms found in the lower section of the estuary to be interrelated. The limitations of using a two-dimensional mathematical and a physical model to predict the complex mixing processes affecting water quality in the Tay Estuary are discussed.

The application of remotely sensed data in the study of frontal systems in the Tay Estuary, Scotland, U.K.

The results of a remote sensing study of tidal mixing processes in the Tay estuary are correlated with the results of mathematical and physical models and ground sampling data in an attempt to assess the nature, the spatial and temporal extent, and the variability in the formation of convergent fronts in the Tay estuary. The application of remote sensing methods to the study of estuarine mixing processes in the Tay Estuary, supported by ground measurements, reveal convergent front mechanisms which had not previously been recognized in the Tay estuary. This integrated approach enables the various features and mixing mechanisms found in the lower section of the estuary to be related. The limitations of using a two-dimensional mathematical and a physical model to predict the complex mixing processes affecting water quality in the Tay Estuary are discussed. The widespread occurrence of convergent systems in the estuarine environment suggests that to obtain an accurate estuarine water quality model, the effect of fronts should be included. The limitations of remote sensing data, the problems of geometrically rectifying airborne imagery in the coastal zone, and two methods of correcting for atmospheric effects in the thermal infrared waveband are also discussed.

Surface runoff, soil erosion and water quality modelling in the Alpone watershed using AGNPS integrated with a Geographic Information System

A modern approach to problems of non-point source water pollution and erosion in a watershed consists in linking distributed models to Geographic Information Systems (GIS). Water quality and quantity are affected by the inherent spatial and time variability of the hydrological attributes within a watershed. Spatially distributed models and data are more suitable than conventional lumped ones. They act directly on spatially distributed data to assess hydrological transport processes affecting water quality. The linkage of GIS is a powerful tool to handle and provide the large amounts of detailed input data that these models require, reducing uncertainty caused by spatial averaging. The AGNPS (Agricultural Non-Point Source) model was used to assess runoff, soil erosion, and associated non-point source pollution for events monitored in the Alpone watershed (Italy). This is an event-based model and operates on a cell basis so that the spatial variation in parameters of each cell can be accounted for in the analysis throughout the whole watershed. Runoff predictions were compared for 20 observed events that occurred in 1992 and 1993. Predictions of sediment yield and nutrient loading were compared with seven observed events. An integrated AGNPS/GIS system was developed to efficiently create the necessary large number of data inputs. Moreover, graphical displays of the results have proven to be a very effective and efficient way of interpreting the results and of decision-making during model calibration. The GIS output layers may be used in planning studies to determine locations, within a watershed, that are critical in sediment yield and in the contribution of pollutant nutrients. The early results of the study point out that the runoff volume is properly estimated by the model while peak runoff rates are poorly predicted, both at low and high values. Predicted nutrient load generally parallels predicted sediment load: in fact in the case of nutrients, overestimation or underestimation are found to extend over the same ranges as those predicted for sediment load by AGNPS. The results from the Alpone watershed have illustrated the capability of the model for estimating sediment and nutrient yields and their spatial distribution particularly in the case of large storm rainfall events, which produce most of the total annual load of sediment and nutrients in the watershed. Nevertheless, the need is felt both of checking the model more carefully and of conducting further studies in order to take into account the considerable space-time variability of rainfall data within the watershed.

Principles for calculation of transport and water quality in strongly regulated reservoirs

Abstract A model system has been generated for the buttom and water quality development of reservoirs during the first few decades of impounding. The model is based on 3D (three-dimensional: longitude × latitude × depth) calculation of the water currents, their variation with time and on 3D description of release, transport, degradation, settling and other processes affecting water quality and the bottom. Special attention in the model development has been paid to the effects of varying water levels and to the internal loading from the bottom. The latter is a combined result of several processes, including degradation of the former terrestial vegetation and organic matter in general, gas development and convective flows, and erosion caused by waves, currents and ice cover. Results from the Porttipahta Reservoir in Finnish Lappland are presented and compared with the field observations as an example of the model applications.

Phosphate adsorption and desorption in relation to morphology and crystal properties of synthetic hematites

Phosphate adsorption and desorption by iron hydr(oxides) are geochemically important processes affecting water quality and soil fertility. Relatively little is known, however, about the interaction between phosphate and hematite, which after goethite is the most abundant iron hydr(oxide) in nature. To study the effect of morphology and other crystal properties of hematite on phosphorous adsorption and desorption, thirty hematites synthesized by different methods and differing widely in properties were used. Phosphate adsorption curves 1 and 124 days after P addition were adequately described by the Freundlich equation. The P adsorbed at an equilibrium concentration of 1 mg P/L (32 μM) at 1 and 124 days ( A 1 , A 124 ) ranged between 0.31 and 2.07 ( X ̄ = 1.03; SD = 0.53) μmol/m 2 , and between 0.54 and 2.72 ( X ̄ = 1.59; SD = 0.65) μmol/m 2 , respectively. The values of A decreased when the crystals and the X-ray coherently scattering domains became more platy in the c with respect to the a direction, supporting the hypothesis that the P-adsorbing faces are the nonbasal ones. Exponent b of the Freundlich equation, which gives a measure of the relative affinity of the adsorption sites, increased when domains and crystals became more platy, i.e., the more platy the crystal, the lower the proportion of high-affinity sites. The ratio between slow (1–124 days) and total (124 days) adsorption increased with decreasing affinity (higher b values) and was not related to microporosity. In comparison to goethite, the present results show that hematite has more variability in P-adsorption capacity, adsorbs on average less P per unit surface area, has less affinity for phosphate, and exhibits a more important slow adsorption component. The proportion of the adsorbed phosphate that could be desorbed by an anion-exchange resin or by electroultrafiltration was affected by those hematite properties affecting diffusion (e.g., microporosity). Isotopically exchangeable P did not depend on morphological or crystalline properties. Irrespective of the method, desorbability, i.e., the proportion of adsorbed phosphate that was desorbable or isotopically exchangeable, was positively correlated to parameter b, suggesting that more desorption occurs in samples having a higher proportion of low-affinity sites. Desorbability was also positively correlated to the ratio between slow and total adsorption. It appears, therefore, that slow adsorption and desorption take place preferentially at low-affinity sites.

Water quality and freshwater fish culture intensification: the Israeli example

. During the development of freshwater fish culture in Israel there has been a trend toward intensification, which has been accelerated in the last years with the introduction of new culture systems: deep reservoirs, fish cages and mechanically stirred ponds. In the present paper, the main processes affecting water quality variability in outdoor systems with increasing fish culture intensification levels are presented. The analysed systems are semi-intensive shallow ponds with different organic loading, semi-intensive shallow ponds with different fish species combinations, semi-intensive deep reservoirs, and intensive mechanically stirred ponds. The examples are from experiments conducted at the Fish and Aquaculture Research Station Dor and from follow-ups at fish farms.

Water Quality and Management Strategies in London's Docklands

ABSTRACTRegeneration and changes in land use in London's Docklands have resulted in new water quality requirements. Areas previously occupied by docks now form part of redevelopment projects which have made a feature of the water.The paper describes a project to provide water that is aesthetically pleasing and of a quality suitable for water contact recreational activities.An extensive programme of water sampling and analysis was carried out to gain an understanding of the processes affecting water quality, including the monitoring of algal growth. The river is the main source of nutrients in the docks, which results in large concentrations of algal biomass and bacterial contamination. The principal strategy is to limit light via artificial mixing systems supplemented by limiting the inflow of nutrients from the river.The results from the water sampling programme have been used to build a 3D computer model with a supporting graphic information system to attain (a) qualitative evaluations of management and development options, and (b) short‐term predictions of changes in water quality.