Measuring atmospheric nutrient deposition to inland waters: Evaluation of direct methods

Several methodological problems have been noted in analyses of atmospheric phosphorus (P) and nitrogen (N) deposition to inland waters. These include the quantification of contamination, rates of dry deposition of nutrients on wet and dry surfaces, and short-range dust contamination. On and around a small lake in an agricultural region, we tested bulk and automated dryand wet-deposition samplers for the presence of insect and dust contamination and presented procedures to eliminate biases. Local (≤100 m) dust deposition appeared negligible, so land-based measurements could be extrapolated to water; however, onand near-shore samplers collected more insect contaminants than off-shore samplers. Insect contamination was large and most significant for estimates of P deposition, but a method to correct for it is proposed. We found that bulk and automated dryand wet-deposition samplers yielded similar values when contamination was eliminated. Screens for atmospheric deposition samplers were tested and led to lowered insect contamination and similar deposition rates to samplers without them. Bulk sampling can provide acceptable estimates of atmospheric nutrient deposition if contamination is quantified or excluded. A wet surface does not differ significantly from a dry surface for measurement of dry-fall of P. Short-range transport of dust-borne nutrients may be insignificant. Low-cost bulk samplers yielded accurate measurements of atmospheric nutrient deposition.