Effects of wave disturbance and substrate slope on sediment characteristics in the littoral zone of small lakes

Sediment characteristics in the littoral zone of lakes affect the distribution, biomass, and productivity of benthic organisms and affect chemical exchanges with the water column, yet we know very little about their distribution. I tested whether sediment water and organic matter content were related to site exposure and to basin morphology by comparing sediments along 12 transects in three small lakes (area <150 ha). The distribution of sediment water content in small lakes differed from the general patterns described for large lakes and ocean. Sediment water content was generally high in shallow waters (<2-5 m), decreased sharply to 30-50% within 20 m from shore, and increased again in the deeper portion of the littoral zone. Fine sediments were retained in the shallow littoral zone (<1.5 m) at sites with mean fetch <150 m. The maximum depth at which sediments were mixed increased with increasing depth of the wave-mixed layer and with increasing slope of the substrate. The organic matter content (OM) of littoral sediments was closely related to their water content (WC) (log(OM) = -4.7 + 3.0 log(WC), r(2) = 0.77, P < 0.001), and sediment organic content was very similar in the upper and lower portions of the littoral zone.