Status of some finfish stocks in the Chesapeake Bay

The Chesapeake Bay is one of the largest and most productive estuaries in the United States. The fish and shellfish harvest in 1979 totaled 284.5 × 10⁶ kg. Although historical measures of stock size are less than optimum, commercial landings and indices of reproductive success indicate declines in several species of anadromous and semi-anadromous finfish. Causes for the declines may be due to point and non-point sources of water pollution, acid deposition or overfishing. The EPA Chesapeake Bay Study identified a number of major environmental problems in the Bay but the exact linkages between environmental problems and fish stocks have not been made.     

Impact of heavy metal amended sewage sludge on forest soils as assessed by bacterial and fungal biosensors

Bacterial and fungal bioluminescence-based biosensors were used as indicators of potential heavy metal toxicity to microorganisms in the needle litter of a mature Pinus radiata forest under heavy metal contaminated sewage sludge. Sewage sludge was amended with increasing concentrations of Cu, Ni and Zn and applied to the surface of a mature P. radiata forest. The response of the bacterial and fungal biosensors to soluble Cu, Ni and Zn in needle litter extracts was investigated. The bioluminescence response of the bacterial biosensor Escherichia coli HB101 pUCD607 declined as water-soluble Zn concentrations increased. The effective concentrations that gave a 50% reduction in bioluminescence (EC₅₀ values) for water-soluble Zn and total litter Zn were 1.3 mg l⁻¹ and 3700 mg kg⁻¹, respectively. The bioluminescence response of the fungal biosensor Armillaria mellea declined as soluble Cu concentrations increased. The EC₅₀ values for water-soluble Cu and total litter Cu were 0.12 mg l⁻¹ and 540 mg kg⁻¹, respectively. No decline in bioluminescence was noted for either the bacterial or fungal biosensor on exposure to increasing concentrations of water-soluble Ni. The use of a combination of bacterial and fungal biosensors offers a rapid and sensitive tool for assessing toxicity of heavy metals to microorganisms and, thus, elucidating the environmental impact of contaminants in sewage sludge on litter dwelling microorganisms.     

Attempts to derive EC50 values for heavy metals from land-applied Cu-, Ni-, and Zn-spiked sewage sludge

We established a field trial to assess the impacts on soil biological properties of application of heavy metal-spiked sewage sludge, with the aim of determining toxicity threshold concentrations of heavy metals in soil. Plots were treated with sludges containing increasing concentrations of Cu, Ni and Zn in order to raise the metal concentrations in the soil by 0-200 mg Cu kg⁻¹, 0-60 mg Ni kg⁻¹ and 0-400 mg Zn kg⁻¹, and were then cultivated and sown in ryegrass-clover pasture and monitored annually for 6 years. All biological properties measured (soil basal respiration, microbial biomass C, and sulphatase enzyme activities), except phosphatase activity, increased in all plots over the duration of the experiment. Consequently, it was only possible to assess effects of heavy metals across time if, each year, all data for each metal were normalised by expressing them as percentages of the activities measured in an un-sludged control plot. When this was done, no significant effects of increasing heavy-metal concentrations on basal respiration, microbial biomass C or respiratory quotient (qCO₂) were observed, although total Cu and soil solution Cu were significantly negatively related to microbial biomass C when it was expressed as a proportion of soil total C. None of the properties measured were affected by increasing Ni concentrations. Phosphatase and sulphatase activities were significantly negatively related to increasing Zn concentrations, but not usually to increasing Cu unless they were expressed as a proportion of total C. A sigmoidal dose-response model was used to calculate EC₂₀ and EC₅₀ values using the normalised data, but generally, the model parameters had very large 95% confidence intervals and/or the fits to the model had small R² values. The factors primarily responsible for confounding these results were site and sample variations not accounted for by the normalisation process and the absence of any data points at metal concentrations beyond the calculated EC₅₀ values. In the few instances where reasonable EC₂₀ values could be calculated, they were relatively consistent across properties, e.g., EC₂₀ for total Zn and phosphatase (330 mg kg⁻¹), total Zn and sulphatase (310 mg kg⁻¹), and EC₂₀ for total Cu and sulphatase (140 mg kg⁻¹) and total Cu and microbial biomass C (140 mg kg⁻¹), when both sulphatase and microbial biomass C were expressed as a proportion of total C. Our results suggest that Cu and Zn at the upper concentrations used in this experiment were possibly having adverse effects on some soil biological properties. However, much higher metal concentrations will be needed to accurately calculate EC₂₀ and EC₅₀ and this may not be easily achievable without many applications of sewage sludge, even if the sludge is spiked with heavy metals.     

Temporal response of soil biochemical properties in a pastoral soil after cultivation following high application rates of undigested sewage sludge

Soil biochemical properties were measured annually between 1995 and 1999 in soil from an 8-ha site that had received over 1,000 wet tonnes ha^–1 undigested sewage sludge, 1–4 years earlier. Basal respiration generally declined with time and was usually greatest in the untreated control area. This trend was attributed to a similar trend in soil moisture content. In contrast, microbial biomass C increased with time and also generally increased with sludge treatment age. Microbial biomass C, and to a lesser extent sulphatase activity, accurately predicted the order of sludge application to the site. This was perceived as a function of time since tillage and pasture establishment, with activities increasing in parallel to the build up of C residues in the soil, and not an effect of sludge or its composition. Except immediately after sludge application, there was no effect on N mineralisation and nitrification. None of the biochemical properties was strongly correlated with heavy metal concentrations. Our results suggest that there was little effect on soil biochemical properties, either adverse or beneficial, of adding raw sewage sludge to this site. Although a companion study showed considerable mobility and plant uptake of heavy metals, this difference could mainly be attributed to a different sampling strategy and the effects of intensive liming of the site.     

Heavy Metals in Soil, Plants and Groundwater Following High-Rate Sewage Sludge Application to Land

The concentrations, solubility and mobility of Cr, Cu, Ni, Pb and Zn were measured over a four year period in soil from a site that had received over 1000 t ha^-1 wet, undigested, sewage sludge (on average, 15% dry solids). The pH of this light-textured sandy soil was markedly reduced after sludge application (to ≤4 in some samples), presumably as a result of breakdown of the unstable organic matter, nitrification of the NH₄ ⁺-N and sulphide oxidation. As a consequence, soil solution concentrations of Cu, Ni, and especially, Zn were initially elevated, and this was reflected in high plant uptake of Zn and elevated levels of all three metals in some groundwater wells. An extensive liming programme resulted in soil pH values generally between 5 and 6, more normal for this soil, in the following years. Soil solution metal concentrations were substantially lower, e.g., Zn from a high of 27 mg kg^-1 in 1995 to 0.04 mg kg^-1 in the equivalent sample in 1999. Herbage Zn concentrations declined accordingly and overall there was a strong relationship between plant metal uptake and soil solution concentration of this element (R² = 0.84), although not for any of the other metals. Our results suggested that, for this soil, pH was by far the greatest determinant of metal solubility and that the metal source, whether sewage sludge or geochemical, had little influence. Results from extractants that solubilise other metal phases, i.e., NaNO₃, EDTA and HNO₃, are also presented and discussed.     

Phosphatase activities of pasture plants and soils: Relationship with plant productivity and soil P fertility indices

Summary Phosphatase activities of herbage roots and soil were measured at low- and high-fertility pasture sites over 12 months. Seasonal trends were examined and relationships with herbage yields, plant P contents, soil moisture and available P were assessed. The phosphatase activities generally followed complex seasonal patterns, although some trends were apparent. At the low-fertility site, where organic P provides most plant P, herbage and root phosphatase activities were correlated significantly (P<0.05) with available organic P, although generally, the plant phosphatases were not good indices of plant yield or P status. Soil moisture content appeared to be the major factor controlling plant phosphatase activity. Herbage phosphatase responded negatively at the low-fertility site, probably as a consequence of lower P availability from dry surface soil. Root phosphatase responded positively at both sites, indicating a different physiological role from that of the herbage enzyme. At the low-fertility site, soil phosphatase was correlated significantly (P<0.05) with herbage yield.     

Examining the integrity of soil metal bioavailability assays in the presence of organic amendments to metal‐spiked soils

This paper questions whether the presence of biosolids amendment in metal‐spiked soils alters the outcome of soil‐based assays of metal bioavailability. The effects of biosolids amendment on the efficacies of six soil metal bioavailability assays (total recoverable, EDTA, Ca(NO₃)₂, soil solution, diffusive gradient in thin films and free ion activity) were assessed against metal concentrations in wheat shoots (Triticum aestivum) germinated in three contrasting soils, each previously incubated for either 2 weeks or 6 months following treatment with Cd, Cu, Ni and Zn +/? biosolids amendment. Overall, Ca(NO₃)₂ was the most accurate method to predict Cd (r² = 0.62), Ni (r² = 0.73) and Zn (r² = 0.55) bioavailability in soils and therefore was used to compare variations in responses between biosolids and nonbiosolids‐amended soils. Comparisons between these two groups revealed no significant differences in linear relationships for all four metals and soil types assessed. These findings not only support Ca(NO₃)₂ as a robust and valid method for determining soil metal bioavailability across metal matrices and soil types, but also that the presence of biosolids does not compromise the predictive power of this assay or any of the others examined.     

Gradient differences in soil metal solubility and uptake by shoots and roots of wheat (T. aestivum)

The aim of this research was to identify and quantify gaps in currents methods and models for predicting the plant availability of selected nutrient and contaminant metals (Cu, Ni, Zn, Cd) in soil. This study investigated relationships between the relative solubility of Cu, Ni, Zn, and Cd determined by six extraction methods with short-term uptake by shoots and roots of wheat (Triticum aestivum). For Cu, Ni, and Cd, relationships between solubility and plant uptake were found to be different for shoots and roots, with Cu and Ni solubility being more closely correlated with root uptake compared with shoot uptake. Correlation coefficients for Cd concentrations in shoot and root tissue for all six solubility methods were poor (r ²?<?0.5), while corresponding results for Zn explained more than 50 % of shoot variation but less than 50 % of root variation. Soil Cu solubility explained up to 85 % of variation in root uptake compared with 42–55 % for shoot uptake. These results clearly demonstrated that purely chemical and passive diffusion mechanisms were inadequate predictors of Cd uptake by shoots and roots, together with Cu uptake by shoots. Thus further attempts at refining soil metal bioavailability assays based solely on chemical extraction without consideration of plant responses are unlikely to improve prediction of plant uptake.     

Impact of pasture contamination by copper,chromium, arsenic timber preservative on soil biological activity

Contamination of grazed pasture gave 0–5 cm soil contents of 19–835 mg kg^-1 Cu, 47–739 mg kg^-1 Cr, and 12–790 mg kg^-1 As. Soil Cu, Cr, As contents were correlated and declined with depth to 30 cm. In plots with medium and high contamination buried cotton strips retained most of their original tensile strength, indicating repression of decomposition processes.Lumbricus rubellus andAporrectodea rosea were absent in plots with medium and high contamination; there was no evidence of heavy metal accumulation in earthworm tissue; soil bulk density was greater in the absence of lumbricids. Enchytraeids and nematodes were most abundant with low contamination. Nematode diversity was greater with low (0–5 cm) or medium (5–10 cm) contamination than in control plots or those with high contamination; the proportion of predators increased with contamination. Basal soil respiration was less sensitive than substrate-induced respiration to contamination. Although contamination reduced the nitrification rate, all mineral N was found as NO _inf3 ^sup- after 14 days. Sulphatase was the enzyme activity most sensitive to high contamination. Whereas contamination by 100 mg kg^-1 of Cu, Cr, and As caused little depression of soil biological activity, there was some supperssion at 400 mg kg^-1 and at 800 mg kg^-1 normal processes were inhibited and herbage production was negligible. No single measurement adequately indicated the need for site remediation.