Dissolved organic matter (DOM) in soils plays an important role in the biogeochemistry of carbon, nitrogen, and phosphorus, in pedogenesis, and in the transport of pollutants in soils. The aim of this review is to summarize the recent literature about controls on DOM concentrations and fluxes in soi

Controls on the dynamics of dissolved organic matter in soils: a review.

Physical, chemical and perceived stressors can all evoke non-specific responses in fish, which are considered adaptive to enable the fish to cope with the disturbance and maintain its homeostatic state. If the stressor is overly severe or long-lasting to the point that the fish is not capable of regaining homeostasis, then the responses themselves may become maladaptive and threaten the fish's health and well-being. Physiological responses to stress are grouped as primary, which include endocrine changes such as in measurable levels of circulating catecholamines and corticosteroids, and secondary, which include changes in features related to metabolism, hydromineral balance, and cardiovascular, respiratory and immune functions. In some instances, the endocrine responses are directly responsible for these secondary responses resulting in changes in concentration of blood constituents, including metabolites and major ions, and, at the cellular level, the expression of heat-shock or stress proteins. Tertiary or whole-animal changes in performance, such as in growth, disease resistance and behavior, can result from the primary and secondary responses and possibly affect survivorship.Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol in actinopterygian fishes, that occur following a stressful event. The characteristic elevation in circulating cortisol during the first hour after an acute disturbance can vary by more than two orders of magnitude among species and genetic history appears to account for much of this interspecific variation. An appreciation of the factors that affect the magnitude, duration and recovery of cortisol and other physiological changes caused by stress in fishes is important for proper interpretation of experimental data and design of effective biological monitoring programs.

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Stress in Fishes: A Diversity of Responses with Particular Reference to Changes in Circulating Corticosteroids

Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

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The Ecology of Phytoplankton

Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.

Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry.

Summary
1. The thermal regime of rivers plays an important role in the overall health of aquatic ecosystems, including water quality issues and the distribution of aquatic species within the river environment. Consequently, for conducting environmental impact assessments as well as for effective fisheries management, it is important to understand the thermal behaviour of rivers and related heat exchange processes.

2. This study reviews the different river thermal processes responsible for water temperature variability on both the temporal (e.g. diel, daily, seasonal) and spatial scales, as well as providing information related to different water temperature models currently found in the literature.

3. Water temperature models are generally classified into three groups: regression, stochastic and deterministic models. Deterministic models employ an energy budget approach to predict river water temperature, whereas regression and stochastic models generally rely on air to water temperature relationships.

4. Water temperature variability can occur naturally or as a result of anthropogenic perturbations, such as thermal pollution, deforestation, flow modification and climate change. Literature information is provided on the thermal regime of rivers in relation to anthropogenic impacts and such information will contribute to the better protection of fish habitat and more efficient fisheries management.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2427.2006.01597.x

The thermal regime of rivers : a review

A unifying model of cation binding by humic substances

Equations are formulated for the standard error and confidence interval for the MPN estimate of microbial density from a general dilution series. A statistical test of homogeneity is presented. This tests whether a handling error in the dilution series may have occurred which would invalidate the density estimate. The analysis may be automated using a Basic computer program which contains a fast algorithm for the solution of the general MPN equation. This allows the calculation of the MPN, standard error, 95% confidence interval and test statistic for any dilution series, with any degree of replication at each dilution level, with variable sample volumes at each dilution level, with variable dilution ratio between levels, and with any number of levels.

Automated statistical analysis of microbial enumeration by dilution series

1. The chief objective was to develop a functional model for the growth of parr (0+, 1+) of Atlantic Salmon, Salmo salar, from two populations (Rivers Leven and Lune in northwest England), using a model similar to that developed previously for Brown Trout, Salmo trutta. Parr bred from Leven parents were acclimatized to nine fairly constant temperatures (two 0+, two 1+ parr per temperature) in the range 3·8–21·7 °C (variation ± 0·3 at 3·8 °C to ± 1·0 at 21·7 °C). Each fish was kept in a separate tank and fed to satiation on shrimps. The mass and length of each fish was recorded at the start and finish of a growth period of 30 days. Parr (0+, 1+) bred from Lune parents were separated into slow and fast growers, and acclimatized to six very constant temperatures. There were three slow and three fast growers at each of 5·0, 10·0, 15·0 °C for 0+ parr and each of 5·0, 10·0, 13·0, 15·0, 18·0, 20·0 °C for 1+ parr. Procedures were the same as for Leven parr except that the growth period lasted 30 days for the 18 0+ parr and 42 days for the 36 1+ parr.



2. The growth model was an excellent fit (P < 0·001) with no significant differences between parr from the two rivers, fast-growing parr of different ages (0+, 1+), or fast- and slow-growing 1+ parr. The optimum temperature for the combined data (81 parr) was 15·9 °C with a range for growth of 6·0–22·5 °C. The model failed to fit the data for slow-growing 0+ Lune parr in experiments from November to February. Growth was reduced in these fish, even though the temperatures were suitable for growth (10, 15°C).



3. The model described approximately the growth of three year-classes of Atlantic Salmon parr in the River Eden in northwest England. Some of the discrepancies between actual masses and those predicted from the model were consistent and possible reasons for this are discussed.

A functional model for maximum growth of Atlantic Salmon parr, Salmo salar, from two populations in northwest England

1. A growth model for brown trout, developed almost 20 years ago, has been used to investigate growth potential in at least 40 populations over a wide geographical range. The chief disadvantages of the model are: it is based on growth data for only 55 hatchery trout kept in tanks without strict control of temperature and oxygen, it is not continuous and is restricted to the range 3.8-19.5 o C, it requires six parameters and only one of these can be interpreted biologically. 2. For the new model, growth data were obtained for an additional 130 trout bred from wild parents and kept in tanks at five constant temperatures (range ±0.1 or 0.2 o C) and 100% oxygen saturation. The new model is continuous over the range 3.8-21.7 o C and has five parameters, all of which can be interpreted in biological terms. It was fitted to growth data for individual fish and was an excellent fit (P 0.99) to the data for the 55 trout of the original experiment, the 130 trout of the new experiment and both experiments combined. The procedure for applying the model to field data is critically examined and a suitable test for maximum growth potential is described. The model ceases to be robust when mean temperatures are estimated over periods of more than 3 months. 3. Although parameter estimates for the new model are similar for the original and new experiments, they are significantly different. An iterative exercise, varying common and different parameters, showed this to be the result of slight differences between two parameters; the optimum temperature for growth and the growth rate of a 1-g fish at this temperature. Possible reasons for this are discussed and it is concluded that these differences have a negligible effect on values predicted from the model

A new, improved growth model for brown trout, Salmo trutta

SUMMARY

CHAOS (Complexation by Humic Acids in Organic Soils) is a quantitative chemical model of organic soils that incorporates complexation by the functional groups of humic substances and non-specific ion-exchange reactions. The two types of interaction are linked by the net humic charge, Z, which depends on the extents of proton and metal complexation, and which in turn determines ionic concentrations in the diffuse part of the electrical double layer, by a Donnan equilibrium. CHAOS was found to account satisfactorily for the results of acid-base titration experiments (pH range 3–5) with soil samples, giving reasonable simultaneous predictions of solution pH and concentration of A13+. Predictive calculations with CHAOS suggest that organic soils acidified by acid rain would respond on a time-scale of years-to-decades to reductions in rain acidity. An associated effect might be an increase in the concentration of dissolved organic matter in the soil solution.

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Margaret Anne Hurley

Papers

A unifying model of cation binding by humic substances

Automated statistical analysis of microbial enumeration by dilution series

A functional model for maximum growth of Atlantic Salmon parr, Salmo salar, from two populations in northwest England

A new, improved growth model for brown trout, Salmo trutta

A model of solid‐solution interactions in acid organic soils, based on the complexation properties of humic substances