Sediment-water oxygen, ammonium and soluble reactive phosphorus fluxes in a turbid freshwater estuary (Curonian lagoon, Lithuania): evidences of benthic microalgal activity

Abstract

Seasonal measurements of total and diffusive benthic fluxes were performed during the ice-free period in the Curonian Lagoon (Lithuania). This mostly freshwater hypertrophic basin exhibits wide seasonal variations of water temperature (1-22°C) and inorganic nitrogen availability and it is subjected to dramatic blooms of diatoms and cyanobacteria (>100 mg chl a L -1 ). In this shallow lagoon, nutrient exchanges at the sediment-water interface and the regulating factors have been poorly explored. Overall aim of the present work is to demonstrate that the activity of benthic microalgae, generally neglected in turbid systems, can be a relevant regulator of sedimentary processes. To this purpose, light and dark fluxes of oxygen, ammonium and soluble reactive phosphorus were measured seasonally by intact core laboratory incubation and diffusive fluxes were calculated from sediment profiles. We investigated sandy sediments that were collected from the central area lagoon, that is representative of the most of the shallower lagoon area.Oxygen and ammonium fluxes were significantly different under light and dark incubations, suggesting an active role of benthic microalgae at the sediment-water interface. In the light net oxygen production was measured in three out of four samplings, with July as only exception, and ammonium was retained within sediments. In the dark sediment respiration displayed a temperature-dependent pattern while ammonium efflux increased from March to October. Fluxes of reactive phosphorus varied significantly with sampling seasons but were less affected by the incubation condition. Diffusive fluxes peaked in July, where highest concentration gradients at the interface and theoretical efflux of ammonium and reactive phosphorous were calculated. The marked differences between diffusive and total nutrient fluxes are probably due to photosynthetic activity by benthic microalgae, and thus oxygen production, enhancement of aerobic processes and net solute uptake at the sediment-water interface. Our findings support the hypothesis that even in highly turbid systems benthic microalgae can have a relevant role as filters for regenerated nutrients and as regulators of benthic processes.

Role of ephemeral vegetation of emerging river bottoms in modulating CO2 exchanges across a temperate large lowland river stretch

“…However, such rates are constrained by the low biomass of algae, much smaller than those of vascular plants. The C sink role of microphytobenthos was demonstrated in a variety of illuminated sediments, where benthic algae assimilate inorganic nutrients both from pore and bottom waters, balancing internal recycling and eutrophication phenomena (Sundbäck et al 2004;Zilius et al 2012). Furthermore, microphytobenthos may persist for several months renewing their sink role in time.…”

Effects of key species mud snail Bullacta exarata (Gastropoda) on oxygen and nutrient fluxes at the sediment-water interface in the Huanghe River Delta, China

“…The MPBs produce enough oxygen to compensate for the oxygen consumed by the heterotrophs in the sediment. The benthic microalgae use nutrients and regulate benthic processes at the sediment-water interface, which are probably due to their photosynthetic activity, oxygen production and enhancement of aerobic processes (Zilius et al, 2012). Another reason was that the key species in the benthic community were often responsible for most of the bioturbation (Davey, 1993).…”

Temporal variability of benthic-pelagic coupling in shallow enclosed environment: A case study with eutrophying shrimp ponds

“…However, this may not always be the case, because a considerable amount of light can reach the sediment at the beginning of the rearing M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT period in this shallow environment. Moreover there is evidence that microphytobenthos may remain viable even if not exposed to light for long periods, and that they are capable of photosynthesis at very low light levels (Sundbäck and Graneli, 1988;Sundbäck et al, 2004;Zilius et al, 2012). Sediment colonized by microphytobenthos can retain nutrients via their assimilation both from the water column and pore water (e.g.…”