Monitoring structural and functional responses of the macroinvertebrate community in a resilient stream after its depollution (Casablanca, Morocco).

Abstract

This study evaluates the changes in the structure of the macroinvertebrate functional feeding groups (FFGs) of the Hassar Stream (northeast of Casablanca) following the installation of Mediouna's wastewater treatment plant (WWTP). Data on water quality and the macroinvertebrate fauna were collected at seven sample points from November 2013 to October 2014. Macroinvertebrates were used to assess the impact of physicochemical and hydromorphological properties on the FFG organization and resilience. Redundancy analysis (RDA) was employed to examine the distribution of FFGs along this stream. Based on the FFGs' relative abundance, collector-gatherers account for 39.06% of the macroinvertebrates' assemblage, followed by shredders (28.41%), collector-filters (18.76%), scrapers (7.16%), and predators (6.6%). The FFG ratios revealed that the environment was highly heterotrophic (P/R < 0.75), and all studied stations had relatively stable substrates. In addition, the ratios indicated that the studied stations had a functional riparian zone (CPOM/FPOM > 0.25), except for stations S1 and S2. Simultaneously, the RDA model revealed that the distribution of the FFGs closely followed fluctuations in the water quality (BOD5, NH4+, PO43-, EC, and Cl-) and hydromorphic properties (flow and depth). These findings highlight the importance of studying macroinvertebrate FFGs as a complementary way to assess the aquatic ecosystems' ecological integrity and resilience following anthropogenic impact reduction.