Influences of stream size and catchment land-use on fine particulate organic matter retention in streams

Using corn pollen as an analogue for fine particulate organic matter (FPOM), retention characteristics were measured for 13 reaches encompassing three different catchment land-use classes (pasture, native forest, and exotic pine forest), and five pasture sites along the Mangaotama Stream, New Zealand. The retention coefficients (specific loss rate, m(-1)) of reaches having similar positions in the stream continuum did not differ significantly between land-use types. The retention coefficient was strongly related to several correlates of position in the stream continuum-notably the logarithm of discharge. We were unable to identify the mechanisms responsible for removing corn pollen from suspension, but loss rates were consistently lower than those predicted from the still-water sinking speeds of the corn pollen.