Phosphorus loss from land to water: integrating agricultural and environmental management

Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased society's awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.     

Towards diagnostic biotic indices for river macroinvertebrates

The construction of biotic indices that use macroinvertebratesto assess pollution and other anthropogenic disturbances ofrivers and streams often requires that each taxon be assigned anumber indicating its level of sensitivity. A problem inconstructing such indices is that individual taxa may varyquite widely in sensivity, depending on the nature of theparticular disturbance. One possible means of overcoming thisproblem is to construct a suite of indices, each assembledusing sensitivity numbers targeted to a particular impact.In order to test this idea, we sampled macroinvertebrates fromrivers in south-eastern Australia subjected to three differenttypes of anthropogenic disturbance: operation of large dams,discharge of effluent from municipal sewage treatment plants,and contamination by metals originating from historical mining.Using macroinvertebrate data from sampling sites with varyinglevels of exposure to disturbance, we developed sensitivitynumbers for macroinvertebrate families for individual riversand combinations of rivers with the same disturbance type.Sensitivity numbers calculated for individual families differedsignificantly according to disturbance type in several cases.Gastropod molluscs (family Thiaridae) were tolerant of dameffects but sensitive to sewage and metals, whereascoenagrionid damselfly nymphs, elmid beetles and ostracods weremost tolerant of sewage. Corydalid alderfly larvae,leptophlebiid mayfly nymphs, lestid damselfly nymphs,libellulid dragonfly nymphs and scirtid beetle larvae weremost tolerant of metals. Indices constructed using sensitivitynumbers for a particular disturbance were generally mostresponsive to that disturbance, but there was considerablegenerality in responses as well as substantial variabilitybetween different rivers with the same disturbance type. Inparticular, macroinvertebrate communities at sites downstreamof dams responded quite variably, probably because ofsubstantial differences in release regimes. We conclude thatthe approach has merit but requires considerable furtherdevelopment and testing, as well as consideration of the levelsof specificity and diagnostic strength that are appropriate orachievable.     

Effects of suspended sediment and desiccation on the benthic tailwater community in the Colorado River, USA

We demonstrated that differences in habitatrequirements by C. glomerata and Oscillatoria havea profound bottom-up influence on the foodweb in thetailwaters below Glen Canyon Dam in the Colorado Riverthrough Grand Canyon National Park, USA. We examinedthe effects of suspended sediment and desiccation onthe colonization sequence of Cladophora glomerata andOscillatoria spp. and the consequent effects onmacroinvertebrates in each algal community in a seriesof reciprocal transplants in the regulated ColoradoRiver, AZ. Our experiments showed that C. glomeratagrows best in continuously submerged, clear-water,stable habitats, whereas Oscillatoria forms densemat-like matrices of trichomes and sand in varialzones and habitats with high suspended sedimentstypical of many southwestern USA streams. Varial zoneconditions have a stronger influence on communitystructure than habitats with high suspended sediments. Recruitment by chironomid larvae was less dependent onC. glomerata and less affected by suspended sedimentand periodic desiccation than Gammarus lacustris. Weestimated the energy from macroinvertebrate biomassassociated with tufts of C. glomerata to be an orderof magnitude higher than that in Oscillatoriamatrices. Therefore, loss of C. glomerata andreplacement of habitat more suitable for Oscillatoriaas a result of regulated flows indirectly reducespotential energy flow in the Colorado Riverfoodweb.     

Short-term effects of aerially-applied fire-suppressant foams on water chemistry and macroinvertebrates in streams after natural wild-fire on Kangaroo Island, South Australia

In remote areas, wild-fires often must be controlled by applying fire-retardants and suppressants dropped from small aircraft. However, impacts of these chemicals on natural stream ecosystems are poorly known. Unintentional aerial application of fire-fighting chemicals (Phos-Chek WD-881 and ForExspan S) onto two small streams during a natural wildfire on Kangaroo Island, South Australia, provided an opportunity to study the short-term effects on water chemistry and aquatic invertebrates. Within 2 weeks of application, samples of water and macroinvertebrates were collected from sites upstream of the application point, within the zone of application, and downstream where burning had been controlled on two streams. Three sites on a reference stream in the same sub-catchment that had been burned by the same fire but without application of fire-suppressants were also sampled. All sites were resampled three months later (within two weeks of the first flushing rains). There were no marked differences in water quality among the sites on the reference stream but in one of the impacted streams where flow had ceased before the fire, dissolved and total phosphorus concentrations were elevated at the site where the fire-suppressants were applied. Phosphorus concentrations were reduced 2–3-fold at this site after brief flushing by rain. Conversely, dissolved and total N and P concentrations at the other impacted stream that flowed permanently did not differ among the sites and there was no evidence for persistent changes to water quality from the applied fire-suppressant foams. Taxon richness was higher at the application and downstream sites than at upstream sites in the two impacted streams. There were also no discernible effects of the fire-suppressants on macroinvertebrate assemblage composition or taxon richness within the two streams two weeks after the chemical application or soon after flushing rains. Assemblage composition in the temporary stream was significantly different from that in the reference and the other impacted stream but also appeared unaffected by the fire-suppressants. The lack of impact on resident stream macroinvertebrates may result partly from their inherent high tolerance to the harsh physical and chemical conditions of these streams, many of which typically cease flow in summer.     

Mesocosm experiments on nutrient and fish effects on shallow lake food webs in a Mediterranean climate

1. Nutrient and fish manipulations in mesocosms were carried out on food‐web interactions in a Mediterranean shallow lake in south‐east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. 2. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear‐water states. 3. Planktivorous fish increased concentrations of soluble reactive phosphorus (SRP). Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. 4. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L^?1 PO₄‐P and 0.6 mg L^?1 NO₃‐N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. 5. Declining water levels during summer favoured plant‐associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. 6. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. 7. The thresholds of nutrient loading and in‐lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality.     

Invertebrates and urban runoff in a small northern stream,Edmonton, Alberta,Canada

The invertebrate fauna of a small northern stream was examined within Edmonton, Alberta. Many invertebrates that were common upstream of the city were absent or rare within the city. In contrast, some tubificids and chironomids were very abundant within the city. Diversity and richness (number of taxa) of the fauna were much lower within Edmonton than upstream, while the total density was much higher within the city. These changes in the urban invertebrate fauna were apparently caused by the discharge of organic materials and silt from storm sewer runoff.Chemical analysis of routinely-collected water samples did not show significant differences between urban and non-urban sites. This was probably due to the sporadic nature of storm sewer runoff. Peak levels of contaminants in the stream were usually missed because of the routine nature of sampling. Aquatic invertebrates, which exhibit long-term responses to sporadic runoff incidents, provided a better indication of stream water quality than did routine chemical monitoring.     

Environmental quality assessment of the St. Clair River as reflected by the distribution of benthic macroinvertebrates in 1985

A benthic macroinvertebrate and sediment chemistry study of the St. Clair River from Lake Huron to Lake St. Clair was conducted in the spring of 1985. The purpose of the. study was to evaluate the environmental quality of the nearshore areas and assess the effectiveness of industrial and municipal abatement programs that have been implemented since 1977.A total of 112 macroinvertebratd taxa was collected from the river. Classification analysis indicated that 7 macroinvertebrate communities were evident in the river. Discriminant analysis suggested that physical habitat characteristics explained the distribution of 4 benthic communities, while sediment contaminants explained the distribution of 3 benthic communities. These analyses showed that the environmental quality of a 12 km stretch of the river along the Canadian shoreline had been degraded, probably by industrial waste discharges and spills. Toxic conditions were evident along the waterfront of Dow Chemical Canada Inc., probably a result of the combined effects of chlorinated organics, oils and greases, and mercury (historical contaminant) in the sediments. In contrast, the invertebrate fauna throughout the remainder of the St. Clair River reflected meso-eutrophic conditions, typical of a large, unstressed river.A comparison of the environmental quality as reflected by the benthic invertebrate fauna in 1985 with that in 1977 suggests that the abatement programs implemented over the past decade have improved the environmental quality along the Canadian side of the river. The total length of river adversely affected by waste discharges from Canadian industries and municipalities decreased from 21 km in 1977 to 12 km in 1985.     

Improving the performance of the EPT Index to accommodate multiple stressors in Afrotropical streams

The EPT index (Ephemeroptera, Plecoptera and Trichoptera) may be skewed by the wide tolerance to multiple stressors of the Baetid, Caenid and Hydropsychid families, which affects the performance of the EPT index as an indicator of multiple stressors in aquatic ecosystems. The effect of the BCH families on the EPT index was evaluated and alternatives were considered to improve its performance. The hypothesis that the removal of the BCH families improves sensitivity of the EPT index to human-induced stressors in streams and rivers was tested. Macroinvertebrates were collected in January–March 2009 at 22 sites in the Nyando and Nzoia Rivers, Lake Victoria basin, Kenya. Nine derivatives and modifications of the EPT index were tested for responses to a disturbance gradient, ranked into three condition categories (reference, intermediate and impaired). The sensitivity of the proportionate abundance derivative of the EPT index improved when the BCH families were removed, whereas that of the richness derivative improved marginally. Other modifications considered performed poorly when compared with the EPT-BCH metrics. Wide distribution of the BCH across all sites, irrespective of the level of disturbance, reduced the sensitivity of the EPT index in the studied streams. The removal of the BCH families enhanced the sensitivity of the index to multiple stressors in Afrotropical streams and rivers.     

Control of River Blindness in West Africa: Case History of Biodiversity in a Disease Control Program

The elimination of river blindness (onchocerciasis) in West Africa has been one of the most successful public health and economic development programs yet conducted. Control was based on aerial application of insecticides to control the aquatic, larval stages of black flies in the Simulium damnosum complex and distribution of ivermectin-based drugs to reduce incidence of the filarial worm, Onchocerca volvulus, that may ultimately result in blindness. Control efforts were long-term (1974–2003), extensive (with as many as 50,000 km of river miles being treated weekly for 12 years or longer), and far-reaching (distribution of drugs to almost 7 million people in 11 West African countries). The challenges and success of the program were strongly related to biodiversity: the vector S. damnosum is actually a complex of several species and subspecies, which vary in their competence in disease transmission; the filarial worm O. volvulus has different forms that vary in their virulence and incidence of producing blindness in humans; maintenance of the biodiversity of the non-target riverine fauna was a prime concern of both the control program and the donor countries that supported it; the main insecticide used to control the black fly vector was derived from a bacterium Bacillus thuringensis israelensis; and the drug used in controlling the filarial worm was derived from a soil-dwelling Streptomyces fungus. Long-term biomonitoring studies indicate that environmental damage (e.g., loss of sensitive taxa) incurred was reversed when insecticide applications ceased.     

Design and implementation of rapid assessment approaches for water resource monitoring using benthic macroinvertebrates

Abstract Benthic macroinvertebrates are the group of organisms most widely used for assessment of water resources. Rapid assessment approaches are intended to be efficient and cost effective; savings are found in reduced sampling and more efficient data analysis. Rapid bioassessment programmes have been quickly accepted and now cover most of the United States (US) and equivalent programmes cover all of the United Kingdom (UK). Rapid bioassessment programmes are designed to screen large regions, pinpointing trouble spots worthy of more detailed attention. Fundamental to all rapid bioassessment methods is the classification of streams so that comparisons can be made between reference areas and areas of concern, or test sites with similar characteristics. Both the UK and US approaches assess habitat characteristics. These characteristics are used to predict the fauna expected at a test site in the UK approach; in the US they are used as an aid to classification and interpretation of aquatic faunal data. Habitat assessments in the US are also used to determine whether poor water quality or degraded habitat are stressing the invertebrate communities. This is a major development in approaches to water resource assessment. In the UK, a model developed using multivariate statistics uses a few environmental variables thought to be unaffected by human activities to predict the fauna expected at a test site. The US approaches analyse data using several indices (or metrics) presumed to represent ecological features of interest. These indices have a range of sensitivities to different kinds of stress and must be calibrated for the area of interest. The two approaches have been developed in isolation but may have much to offer each other. Developing programmes are advised to consider both. Future needs include: development of procedures that can be applied to large rivers and to lakes; further refinement of ecological principles underlying metric choice; the inclusion of chemical criteria and toxicity tests to establish thresholds that indicate impairment; and development of criteria indicating the necessity for implementation of quantitative assessment studies.     

The ecological integrity of the lower Olifants River,Limpopo province,South Africa: 2009–2015 – Part B: Tributaries of the Olifants River

Monitoring on the Lowveld reaches of the Olifants River, Limpopo River System, and its Steelpoort, Blyde, Klaserie and Selati tributaries was initiated in 2009. Analysis of the 2009–2015 data from four Olifants River sites showed deterioration in the river’s ecological condition between where it enters the Lowveld and where it enters the Kruger National Park, with a slight recovery within the Kruger National Park. Physico-chemical, aquatic macroinvertebrate and fish data collected in 2009–2015 at six sites on the Steelpoort, Blyde, Klaserie and Selati tributaries of the Olifants River corroborated the ecological condition of these tributaries. The Selati was the most polluted and was in a critically modified condition, whereas the Klaserie and Steelpoort were in fair condition and the Blyde was in good condition. The Selati appeared to have a significant negative impact on the water quality, macroinvertebrates and fish of the Olifants River within the Kruger National Park.     

The ecological integrity of the Lower Olifants River,Limpopo province,South Africa: 2009–2015 – Part A: Olifants River main stem

The major rivers of the South African ‘Lowveld’ (low-latitude savanna) suffer numerous impacts from upstream economic activities. Whereas monitoring these rivers is required to detect biodiversity losses, record pollution events and devise mitigation strategies, current monitoring programmes are inadequate. In 2009, the South African Earth Observation Network initiated an intensive long-term research programme on the Lowveld reaches of the Olifants River. Physico-chemical parameters, aquatic macroinvertebrates and fish abundances were recorded at four Lowveld sites in the Olifants River. We review six years of this programme. The results suggest deterioration in the ecological condition of the Olifants River with no discernible improvement through protected areas. Trends could not be detected. The parameters measured, sampling methods and/or sampling frequency might be responsible for the limited trends observed, or alternatively the results simply reflect stable conditions despite on-going pollution. Real time monitoring and an expansion in the parameters monitored would add value to the monitoring programme.     

Rapid assessment of rivers using macroinvertebrates: Case studies in the Nepean River and Blue Mountains,NSW

Abstract Two sets of data were used to evaluate the procedure for rapid assessment of rivers described by Chessman (1995): (i) 72 samples from four habitats at 27 sites on the Nepean River and tributaries; and (ii) 41 riffle samples from the Blue Mountains. In the Nepean system all the sites had moderate anthropogenic disturbance but none had gross organic pollution. There were, however, conductivity differences related to mixed sandstone and shale lithology. The sites differed widely in natural physical attributes such as stream order (2–6) and altitude (40–600 m). The Blue Mountains data included sites with little or no anthropogenic disturbance and sites greatly affected by organic pollution. There was again a wide range of altitudes (15–1000 m) but stream orders were more restricted (1–4). The occurrence of macroinvertebrate families was analysed using cluster analysis (TWINSPAN) and ordination (semi-strong hybrid multidimensional scaling). Relationships between the patterns observed, the SIGNAL biotic index, and physical and chemical data were investigated. The Nepean data showed that the sample size of 100 animals used in the rapid procedure was sufficient to reveal natural distribution patterns in the communities, and that SIGNAL was essentially independent of these patterns. In the Blue Mountains, water pollution had a greater effect on macroinvertebrate communities than the physical habitat, and SIGNAL distinguished sites with differing levels of pollution.     

Resuspension of algal cells by benthivorous fish boosts phytoplankton biomass and alters community structure in shallow lakes

1. Positive effects of fish on algal biomass have variously been attributed to cascading top‐down effects and to nutrient enrichment by fish excretion. 2. Here, we used a combination of field and laboratory approaches to test an additional hypothesis, namely that the physical resuspension of settled algal cells by fish enhances algal biomass and alters community composition. 3. A multi‐lake survey showed that phytoplankton biomass and the fraction of motile algae increased with the concentration of inorganic suspended solids. This correlation could not be explained by wind‐induced resuspension because of the small size of the lakes. 4. In an enclosure experiment, chlorophyll‐a concentration, phytoplankton abundance and inorganic suspended solids increased significantly in the presence of Cyprinus carpio (common carp), but only if the fish had access to the sediment. No such effects were seen when a net prevented carp reaching the sediment. 5. The effects of enhanced nutrients and reduced zooplankton grazing as a result of fish feeding could not (fully) explain these observations, suggesting that the resuspension by carp of settled algae from a surface film on the sediment was the major factor in the outcome of the experiment. 6. An increase in diatoms and green algae (organisms with a relatively large sedimentation velocity) only in enclosures where carp could reach the sediment supported this view. 7. Several lines of evidence indicate that fish‐induced resuspension of algal cells from the sediment is an important mechanism that affects phytoplankton biomass and community composition in shallow lakes.     

Variations in the water quality of a small urban tropical catchment: implications for load estimation and water quality monitoring

This paper presents findings on the quality of runoff draining a small urban tropical catchment in Singapore. Variations in runoff quality were studied by continuous, regular and storm event water sampling over a period of eleven months for suspended sediment, nutrient and inorganic variables. Storm events and anthropogenic activities exerted the most influence on runoff quality. Concentration-discharge rating relationships were derived to assess the rating curve method for calculating load of the variables monitored. The poor rating relationships obtained indicated that the method was not suitable for load estimation in this catchment. Instead, an interpolation method was used to calculate sediment loads. The preliminary results highlighted the importance of conducting small-scale, relatively short-term studies to identify and assess specific water quality problems facing each catchment. Such a sampling strategy might be more useful than either routine or continuous sampling in the context of planning more detailed monitoring strategies and management options suitable for disturbed catchments.     

The Moral Economy of Tobacco

ABSTRACT   Even faced with overwhelming evidence that tobacco threatens human health, along with economic developments undermining their status as independent producers, North Carolina tobacco farmers view tobacco production in ways congruent with a moral economy. A shift from independent to contract production of tobacco and the dismantling of government price supports have challenged this moral economy, converting tobacco producers into a quasi–working class dependent on tobacco companies while leading to fewer tobacco farms and an increase in the average tobacco farm's size. These changes signal a shift away from a moral economy of tobacco, although moral-economic dimensions remain. Producers today emphasize different moral dimensions of economic behavior, such as producing quality human beings, than during earlier eras, when moral-economic actors pressed for state intervention in economic crises. Moral-economic principles are not restricted to either non-Western or historical peoples but, rather, influence economic production and ideology in advanced capitalist settings today.     

Using transplanted oyster (Crassostrea virginica) beds to improve water quality in small tidal creeks: a pilot study

The Eastern oyster, Crassostrea virginica, may improve water quality by filtering large quantities of particulate matter (both organic and inorganic) and nutrients from the overlying water column. Additionally, oyster reefs alter hydrodynamic conditions, further increasing the removal of particulate matter from the water column. This study examined the effects of small-scale oyster additions on sediment loading, chlorophyll a, nutrient concentrations, and flow in small tidal creeks. Two reefs were established in Hewletts Creek, New Hanover County, North Carolina. Total suspended solids (TSS), chlorophyll a, and ammonium were measured upstream and downstream of each created reef and in an adjacent control channel that lacked a reef. Data were collected monthly during ebb tides over a 10-month period between September 2000 and June 2001. In the first month after initial reef placement, mean TSS concentrations downstream of reef placement were slightly lower than those upstream of the reef. Although not statistically significant, TSS concentrations downstream of the reefs were less than upstream concentrations for five out of nine and five out of seven post-reef sampling months for the upland and the lower creek sites, respectively. Chlorophyll a concentrations were not significantly affected by initial reef placement (2×3 m), but were reduced substantially after reef enlargement (3×4 m) in one of the experimental creeks. Reef placement resulted in significant increases in ammonium concentrations downstream of the transplanted-reefs. In addition, deposition of feces and pseudofeces by the oysters resulted in accumulation of finer-grained materials in the treated channel relative to the control channels. Oyster filtration was most effective three hours following high tide, when the ratio of flow discharge to reef surface area was the highest. This work demonstrates that small oyster reefs established and maintained in some small tributary channels can reduce TSS and chlorophyll a concentrations and that the magnitude of the effect may vary over the course of the tidal cycle.