Mark D. Mattson

Redox reactions of organic matter decomposition in a soft water lake

During a three year study (1985–1987) we used a mass balance approach to study the oxidation and reduction reactions related to decomposition of organic carbon in Mirror Lake, New Hampshire. The stoichiometry of the reactions allows us to calculate an electron transfer budget for the summer stratification period in the lake, as well as in benthic chambers and sealed jars.The average decomposition rate measured as dissolved inorganic carbon (DIC) production was 5.33 mmol m−2 d−1. The proportions of decomposition accounted for by the various electron acceptors varied both during the summer, as well as from year to year. On average, oxygen accounted for 43% of DIC production, while the processes involving sulfate, nitrate, iron and methane formation together accounted for 20%. Despite conservative assumptions we could not account for 37% of the DIC production. The general pattern, including excess DIC production, was also observed in chamber studies conducted over shallow-water sediments and in sealed-jar experiments.Data on burial rates of reduced iron minerals indicate that such minerals are not sufficient to account for the discrepancy in the electron budget. Our analysis suggests that another electron acceptor such as organic carbon reduction, either via fermentation or selective oxidation, is the most likely explanation of excess DIC production.

Identification of road salt contamination using multiple regression and GIS

A multiple regression model of atmospheric deposition of salt, combined with geographic information systems (GIS) data on four classes of roads, is used to predict sodium concentrations in 162 randomly chosen streams in Massachusetts. All four classes of roads, as well as atmospheric deposition, were found to be highly significant in a model that explains 68% of the observed variation in sodium concentration. The highest salt loading rates are associated with interstate and major state roads with an estimated 22,500 and 17,700 kg of salt per kilometer, respectively. Our mass balance calculations indicate road salt is the major source of salt to the streams in Massachusetts.We examined some of the common statistical problems associated with the use of multiple regression for this type of analysis. Our confidence in the accuracy of the loading rates estimated above are limited by the collinear nature of environmental data and uncertainties related to model specification. Our results suggest multiple regression techniques can lead to overconfidence in the accuracy of the estimated loading rates and thus should not be used as the basis for policy unless the model is validated.

EVIDENCE OF RECOVERY FROM ACIDIFICATION IN MASSACHUSETTS STREAMS

A ten year survey of water quality in 330 Massachusetts streams was conducted to examine the rate and pattern of recovery from acidification. Meta-analysis was used to combine the results of the 330 non-parametric trend tests into an overall test for trend in a variety of water quality variables including pH, acid neutralizing capacity (ANC), and major inorganic ions. Analysis of trends in the raw data indicates both pH and ANC are increasing. After detrending for variations in stream runoff, we estimate the streams are recovering from acidification at a rate of +0.021 pH units/year and +2.4μeq/L/year, for pH and ANC respectively. These trends appear to be related to declines in sulfate (−1.8μeq/L/year), while base cation trends were mixed. Meta-analysis reveals the trends are not always homogeneous between seasons or between sites.While it is commonly assumed that the low ANC systems are most ‘sensitive’ to changes in acid or base inputs, we found the greatest rates of change in ANC were associated with the high ANC systems. The greatest increases in pH were seen in the low ANC streams as expected. The results also suggest streams respond quickly to changes in precipitation inputs and stream monitoring networks may be valuable as an early detection technique for changes in environmental quality.

Acidity status of surface waters in Massachusetts

The Massachusetts Acid Rain Monitoring project surveyed 80.5% of the states 5294 named water bodies between 1983 and 1985. PH and acid neutralizing capacity (ANC) were measured monthly the first 14 mo and semi-annually afterwards. Sample collection and analysis were performed by volunteers. The majority of surface waters in Massachusetts were found to be sensitive to possible long term acidification, with 63% exhibiting ANC less than 200 μeq L−1 and 22% with ANC less than 40 μeq L−1. Seasonal patterns in ANC were observed, the median ANC being 384 μeq L−1 in summer/fall and 134 μeq L−1 in winter/spring. Geographical differences were also found across the state: the streams and lakes with lowest pH and ANC were located in the southeastern and north-central parts of the state, while the most alkaline surface waters were found in the western-most part of the state, which is the only area of the state with significant limestone deposits.