Hadas Lubinevsky, Moshe Tom
The studied region is a sewage-sludge disposal area on sandy-silty shelf bottom of the Mediterranean coast of Israel. Sediment was annually sampled in spring and fall by a box corer and macrofaunal abundance, taxa composition, taxa richness and total organic carbon (TOC) were monitored for the 2011-2022 period, including the sewage-sludge disposal cessation event in March 2017. The study is aimed at describing and interpreting spatial and temporal changes of the evaluated parameters, in the context of disposal cessation and another identified effector. The overwhelmingly dominant taxa during the sewage-sludge disposal period (prior to March 2017) were one or more opportunistic capitellid Polychaeta. An annual cycle of sewage-sludge accumulation in the summer and dispersion by the winter storms was responsible for the annual cycle of abundance. The accumulated sewage-sludge in fall overrode the effect of other factors, prominently attenuated the macrofaunal abundance. TOC levels were stable and relatively high year-round, during the disposal period, and attenuated to background levels a year after its cessation. Complex gradual abundance changes, attenuation of the opportunistic capitellids and entrance of a variety of other taxa, reflected by changes in taxa richness, occurred between 2012 and 2017. These events were not timed with the cessation of sewage-sludge disposal and initially hypothesized to be triggered by seawater warming. In 2018 the disposal area returned to a new steady state of low abundance, relatively high taxa richness, new stable taxa composition and low TOC levels, clearly showing nullification of the sewage-sludge disposal influence.