Effects of mining activities on fish communities and food web dynamics
in a lowland river
Abstract
Fish communities of streams and rivers might substantially be subsidized
by terrestrial insects that fall into the water. Although such
animal-mediated fluxes are increasingly recognized, little is known on
how anthropogenic perturbations may influence the strength of such
exchanges. Intense land-use, such as lignite mining may impact a river
ecosystem due to the flocculation of iron (III) oxides, and thus
altering food web dynamics. We compared sections of the River Spree in
North-East Germany that were greatly influenced by iron oxides with
sections located below a dam where passive remediation technologies are
applied. Compared to locations below the dam, the abundance of benthic
macroinvertebrates at locations of high iron concentrations above the
dam was significantly reduced. Similarly, catch per unit effort of all
fishes was significantly higher in locations below the dam compared to
locations above the dam and juveniles of piscivorous pike Esox lucius
were significantly smaller in size in sections of high iron
concentrations. Using an estimate of short-term (i.e., metabarcoding of
the gut content) as well as longer-term (i.e., hydrogen stable isotopes)
resource use, we could demonstrate that two of the three most abundant
fish species, perch Perca fluviatilis, and bleak Alburnus alburnus,
received higher contributions of terrestrial insects to their diet at
locations of high iron concentration. In summary, lotic food webs above
and below the dam greatly differed in the overall structure with respect
to the energy available for the highest tropic levels and the
contribution of terrestrial insects to the diet of omnivorous fish.
Therefore, human-induced environmental perturbation such as river
damming and mining activities represent strong pressures that can alter
the flow of energy between aquatic and terrestrial systems, indicating a
broad impact on the landscape level.