Leaf litter breakdown in Mediterranean streams: effect of dissolved inorganic nutrients

Abstract

Agricultural runoff and urban activities can increase the inputs of nitrogen (N) and phosphorus (P), into headwater streams, leading to eutrophication and thus substantially affecting the structure and functions of benthic communities. A high P concentration in water stimulates the activity of heterotrophic microorganisms associated with leaf litter and, hence, influences decomposition rates and the availability of detrital resources for macroinvertebrates. Litter breakdown of alder (Alnus glutinosa) leaves enclosed in coarse mesh bags was studied in five low-order Mediterranean streams with different trophic status defined by their soluble reactive phosphorus (SRP) concentrations. Decomposition rates differed significantly between these streams and increased with the eutrophication gradient, but these differences were not always related to the availability of P in water. Leaf mass loss was directly correlated with shredder density, but macroinvertebrate density and diversity were not related to P availability in water, and ammonium concentration had a negative effect on macroinvertebrate diversity and shredder relative abundance. A significantly positive effect of nitrate concentration in water on aquatic hyphomycete sporulation rates was observed, but there also was a negative effect of % ammonium on dissolved inorganic nitrogen (DIN). The predominantly available ionic form of DIN could thus affect the structure of the aquatic hyphomycete community. These results suggest that the response of litter decomposition to eutrophication in forested headwater streams is strongly influenced by local stream characteristics and by the nature of nutrient pollution.

Urbanisation reduces litter breakdown rates and affects benthic invertebrate structure in Pampean streams

“…Although there was a neat negative effect of urbanisation on leaf litter decay, the decay rates in our study were related to water-nutrient content depending on the chemical identity (i.e., DIN or SRP (Englert, Zubrod, Schulz, & Bundschuh, 2013;Fleituch, 2013;Zubrod et al, 2015). However, urbanisation increased decay rates in temperate streams in Appalachian mountains (Gulis & Suberkropp, 2003b), low mountain areas (Pascoal, Cássio, Marcotegui, Sanz, & Gomes, 2005;Rossi et al, 2019), Mediterranean areas (Menéndez et al, 2011), and temperate deciduous forest (Cook & Hoellein, 2016). Even though we might speculate that enriched streams tend to reduce their decay rate, and poor nutrients streams' decay rates are enhanced by urban inputs; decay rates are also affected by previous to urbanization conditions, biome characteristics, and leaf litter species.…”

“…Similar results were found in forested tropical urban streams (Martins, Couceiro, Melo, Moreira, & Hamada, ; Silva‐Junior, Moulton, Boëchat, & Gücker, with sites composed of urban and agricultural uses), tropical high‐altitude Andean urban streams (Iñiguez‐Armijos et al, ), and temperate hills zones after a urban wastewater plant (Englert, Zubrod, Schulz, & Bundschuh, ; Fleituch, ; Zubrod et al, ). However, urbanisation increased decay rates in temperate streams in Appalachian mountains (Gulis & Suberkropp, ), low mountain areas (Pascoal, Cássio, Marcotegui, Sanz, & Gomes, ; Rossi et al, ), Mediterranean areas (Menéndez et al, ), and temperate deciduous forest (Cook & Hoellein, ). Even though we might speculate that enriched streams tend to reduce their decay rate, and poor nutrients streams' decay rates are enhanced by urban inputs; decay rates are also affected by previous to urbanization conditions, biome characteristics, and leaf litter species.…”

“…Chironomus sp. might tolerate oxygen depletion and fine-sediment deposition associated with anoxic conditions, which are characteristics of urban streams (Menéndez et al, 2011;Nelson & Booth, 2002;Pascoal et al, 2005).…”

“…Considering urbanisation in its broadest definition as a process of population concentration (Menéndez, Descals, Riera, & Moya, ), we aimed at assessing urbanisation effects on two proxies of stream integrity: Leaf litter decay and benthic invertebrate assemblage colonizing litter in streams draining urbanised versus reference grassland areas. We hypothesized that (a) leaf litter decay rates and (b) stream invertebrate assemblages colonizing leaf litter are negatively affected by nutrient enrichment and direct channel interventions (i.e., riparian and aquatic plant removal, channelization) resulting from urbanisation.…”

Heterogeneity in leaf litter decomposition in a temporary Mediterranean stream during flow fragmentation

“…Our results revealed a decrease in the C: N molar ratio in leaf litter during decomposition as a result of a gradual increase in nitrogen that occurred while carbon concentration remained practically constant. Other studies have found a similar pattern (e.g., Gulis and Suberkropp, 2003;Pascoal and Cássio, 2004;Menéndez et al, 2011) and have associated it with the accumulation of microbial biomass on leaves that uptake and immobilize nitrogen from the water column as carbon is mineralized (Melillo et al, 1984;Chauvet, 1987). The mineralized litter carbon is replaced by microbial cells, which explains the small changes observed in carbon concentration (Yoshimura et al, 2010).…”