Quantity and composition of stream dissolved organic matter in the watershed of Conesus Lake, New York

Dissolved organic matter (DOM) is a complex mixture of soluble organic compounds that plays important roles in stream ecosystem function. We examined temporal and spatial variation in stream DOM characteristics in the small watersheds draining into Conesus Lake, New York, USA. While all watersheds were impacted by human activity, our study sites spanned multiple land uses, with distinct differences in the proportion of agriculture and natural land cover. Concentrations of dissolved organic carbon and inorganic and organic nitrogen and phosphorus were measured seasonally, with a more detailed analysis during the growing season. DOM composition was assessed with a suite of optical indices and multidimensional fluorescence with parallel factor analysis. Seasonal shifts in the composition and quantity of DOM, characterized by increased protein-like fluorescence in the growing season and maximum DOC concentrations in the fall, were consistent with abiotic seasonal controls and the seasonal influx of allochthonous organic matter to all streams. However, agriculturally dominated streams had higher inorganic nutrients, along with less-humified, less-molecularly complex, and more protein-like fluorescent DOM than those with less agriculture, suggesting that nutrients may be stimulating greater in-stream DOM production. Stream order also played a strong role, with more similarity in the DOM pools in second order streams, consistent with high in-stream processing of both allochthonous and autochthonous DOM. We conclude that agriculture is an important driver of stream water nutrients and the quantity and composition of DOM, in conjunction with abiotic seasonal drivers and in-stream processing time.