Improved methods for the measurement of dissolved and particulate organic carbon in fresh water and their application to chalk streams

Abstract

Summary The development and use of an improved automatic system for the accurate measurement of dissolved organic carbon (D.O.C.) in fresh waters is described. The method, which covers the range 0‐25 mgl−1 D.O.C., is based on the oxidation of organic carbon to carbon dioxide by U.V. radiation. The carbon dioxide produced is measured by a non dispersive infra‐red gas analyser (I.R.G.A.). The I.R.G.A. is also used in the semi‐automatic measurement of particulate organic carbon (P.O.C.) by a combustion method which allows very low concentrations to be measured using samples of 200 ml or less. Results of surveys of two river systems indicate that D.O.C. concentrations of less than 2.0 mg l−1 are typical in unpolluted chalk streams. D.O.C. concentrations of streams draining acid heathland were found to be significantly higher (3‐5.5 mg l−1). D.O.C. concentration was found to increase rapidly during a spate, in a river draining areas of mixed underlying geology. The throughput of D.O.C. during the twenty‐five to fifty spates which occur annually in the river could amount to 20‐30% of the annual flux of D.O.C. P.O.C. concentration in chalk spring waters (0.03–0.04 mg l−1) were found to be higher than expected from preliminary estimates using membrane filtration techniques. The relevance of the measurement of D.O.C. and P.O.C. flux to estimates of the energy budgets of stream ecosystems is discussed and published methods for the automatic measurement of D.O.C. are reviewed.

Potential of turbidity monitoring for measuring the transport of suspended solids in streams

“…The available evidence indicates that water colour [or the concentration of gilvin or dissolved organic carbon (DOC)] increases during storm event runoff and gradually decreases as discharge recedes (Baker et al, 1974;McDowell and Fisher, 1976;Larson, 1978;Lush and Hynes, 1978;Dahm, 1981;Foster and Grieve, 1982;Tate and Meyer, 1983;Grieve, 1984;Eshleman and Hemond, 1985;Bowles et al, 1986;Taylor and Adams, 1986;Lawrence et al, 1988;McDowell and Likens: 1988;Gippel, 1989a). Gilvin and the suspended solids concentration have different source areas (Gippel, 1987) and temporal variations in their concentration are probably only broadly related (Gippel, 1989a).…”

Observations on the ecology of Simuliidae from the River Frome, Dorset

“…A. number of factors may influence distribution patterns; for example, the annual temperature fluctuations are least at upstream stations (Table 2) material) is often lower in the smallest streams, particularly in the summer months. Particulate carbon concentrations usually increase in the lower reaches of the tributaries and in the upper sections of the main River Frome (Farr, personal communication;Baker et al, 1974). Anderson & Dicke (1 960) have suggested that the larvae of certain species of Simulium are less able to tolerate high levels of suspended solids than others.…”

A model for accurate drift estimation in streams

“…Waters (1969) mentions problems with reductions in net filtration performance associated with net ‘clogging’, yet apart from a study of bed drift in an organic‐rich stream undertaken by Malmqvist, Nilsson & Svensson (1978), few of the published studies of riverine drift (taken here to include the drift of fish eggs and larvae, larger fish, and/or invertebrates) have accounted for the clogging effect of organic detritus. This is a surprising omission bearing in mind that chalk streams often carry a considerable load of coarse particulate organic material (CPOM) (Baker et al ., 1974; Bilby & Likens, 1979; Farr & Clarke, 1984; Cuffney & Wallace, 1988). Particularly in mesotrophic chalk streams, the inadvertent trapping of filamentous algae and other CPOM in the nets along with the animal under investigation is often inevitable, necessitating the painstaking separation of sample from organic and mineral debris after each sampling.…”