Detritus accumulation and decomposition in a coastal lake (Acquatina–southern Italy)

Abstract

1. Knowledge about processes and dynamics underlying organic matter accumulation in transitional waters is crucial for the protection of these ecologically important coastal habitats. This study investigated the relationship between large particle accumulation and decomposition in a coastal lake included in a Site of Community Interest (SCI) using sediment trap and litterbag techniques. 2. Two sets of sediment traps were deployed at five sites along the longitudinal axis of the lake. One set was emptied once a month for 12 months, and the other twice a year. The contents of the monthly and the 6-monthly traps and the superficial sediments were then compared to estimate the organic matter accumulation and loss. To determine the mass loss rate of the three major allochthonous sources of detritus (the reed Phragmites australis, the cordgrass Spartina juncea, and the seagrass Posidonia oceanica), litterbags were placed near the sediment traps at three out of the five sites at the beginning of each 6-month period and retrieved monthly. 3. The amount of annual particulate organic matter (POM) deposition in the traps was 1320.2 +/- 58.5 g m(-2) y(-1) and consisted of 25% large particles (CPOM). Allochthonous litter comprised an important fraction of CPOM, and its breakdown rate changed with the plant species, site and season. Loss rate of CPOM accumulated at the lake bottom was significantly related with the mass loss rate of reed and cordgrass litter, but not with that of seagrass. 4. Due to slow litter breakdown and tidal landward advection, the lake acted as a sediment trap for allochthonous matter, especially from Posidonia. The important role of marine-derived litter in organic matter sedimentation suggests addressing conservation strategies of the lake functioning towards the selective control of allochthonous CPOM inputs, in particular at the mouth where the incoming tide brings suspended material and salinity decelerates matter flow to the sea and decomposition. This study supports the hypothesis that sedimentation and decomposition dynamics are important factors for coastal lake evolution, and shows litterbag and sediment trap techniques as simple useful investigation tools in management strategies aiming at conserving transitional waters

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake

“…Pace et al (2004) and Costantini et al (2008) found a strong dependency of detritus accumulation on allochthonous primary producers in both brackish and freshwater ecosystems. Osleger et al (2008) observed that land use around Clear Lake strongly influenced the chemistry of sediments and cyanobacterial population structure.…”

Predator and detritivore niche width helps to explain biocomplexity of experimental detritus-based food webs in four aquatic and terrestrial ecosystems

“…Ultimately, these differences arise from the different chemical composition of autotrophs, which influences consumption by heterotrophs (Cebrian and Lartigue, 2004;Chase, 2000;Costantini et al, 2008;Nowlin et al, 2008;Shurin et al, 2006). The source, quantity and quality of detritus affect the population density, feeding rates and trophic niche of detritivores and thus their interactions with other species in the web.…”

Bridging between litterbags and whole-ecosystem experiments: a new approach for studying lake sediments

“…By contrast, relocating field-collected sediments to new settings, such as the laboratory, may fail to replicate in situ conditions (Orihel and Rooney, 2012). Second, our approach offers a more realistic simulation of long-term mineralisation and decomposition processes than, for example, leaf litterbags, which have been widely used to study biogeochemistry and ecosystem metabolism (Herbst, 1980;Jackson et al, 1995;Longhi et al, 2008;Costantini et al, 2009 The only studies performed at a whole-ecosystem level have focused on removing entire sediment horizons, such as for lake restoration or fisheries management, without manipulating OM directly (Peterson, 1982). New approaches are therefore needed to manipulate natural sediments over large spatial scales.…”

“…Ecological studies have rarely manipulated sediments that have been standardised to mimic natural conditions, despite this strategy being fundamental to fields such as environmental toxicology (Suedel and Rodgers, 1994; but see Feuchtmayr et al, 2009). Traditionally, studies have added OM either to fieldcollected sediments, which have been relocated to laboratories or outdoor mesocosms (Wood and Richardson, 2009;Liboriussen et al, 2011;Song et al, 2013), or in situ by burying decomposing leaves into sediment surfaces (Herbst, 1980;Jackson et al, 1995;Longhi et al, 2008;Costantini et al, 2009;Marmonier et al, 2010).…”