Leaf litter processing rates in a Kenyan highland stream, the Njoro River (original) (raw)
Leaf-litter budgets in two contrasted forested streams
Limnetica
SUMMARY Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a deciduous forest and the other one flo- wing under an Eucalyptus globulus plantation. Inputs (vertical and lateral) of terrestrial CPOM to the streams, and CPOM storage in each stream bed were measured from September 93 to September 94. A model incorporating leaf-litter storage, terrestrial inputs and break- down rates was applied to study leaf-litter dynamics in both streams. The relative importance of breakdown and transport as proceses affecting the availability of leaf-litter in the stream bed was assessed. Our data suggest that 10-17 % of leaf litter entering these streams annually is processed in place. Significant relationships between organic matter storage and the rate of terrestrial input were found at both cites. However, because of the different timing of leaf fa11 between both forest types, relationships between stream flow and leaf-lit- ter storage were site-dependent...
LEAF-LITTER BUDGETS IN TWO CONTRASTING FORESTED STREAMS
2000
SUMMARY Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a deciduous forest and the other one flo- wing under an Eucalyptus globulus plantation. Inputs (vertical and lateral) of terrestrial CPOM to the streams, and CPOM storage in each stream bed were measured from September 93 to September 94. A model incorporating leaf-litter storage, terrestrial inputs
Leaf litter transport and retention in a tropical Rift Valley stream: an experimental approach
Hydrobiologia, 2001
The dynamics of leaf litter transport and retention in two contrasting reaches in the Njoro River, Kenya, is reported, analysed and discussed. The study focussed on two aspects: experimental leaf litter transport and retention in the Maryjoy and Turkana reaches which differ in structural heterogeneity and natural leaf litter transport in the two reaches. Leaves of Dombeya goetzenii, Syzygium cordatum and Grewia forbesii were dyed differently with ‘Herbol®’ dyes and used to elucidate the dynamics of leaf transport and retention. Experimentally, about 40% of each of the three leaf species released into the water column travelled beyond the experimental 50-m mark in the Maryjoy reach (devoid of major retention structures) and about 95% of the leaves were retained within the Turkana reach (with major retention structures) and never reached the 50-m mark. Based on the calculated average leaf travel distance (1/k), the leaves of D. goetzenii could have drifted 10–113 m in the Turkana reach and between 60 and 127 m in the Maryjoy reach. The transport trends of the three leaf species were reach- but not leaf species-specific. The efficiency of trapping the drifting leaves differed from one retention structure to another in both reaches. Rock outcrops and debris dams were the main descriptors of the stream heterogeneity in the Turkana reach and retained about 55% and 20% of the experimental leaves, respectively. The leaves of S. cordatum dominated the leaf litter transported naturally within the two reaches, contributing 214.4±18.7 g d−1 to 274.1±36.8 g d−1 (± standard error) of the leaf litter biomass in the Turkana reach. It was estimated that 640.9 kg of leaf litter are exported to Lake Nakuru by the Njoro River annually.
Litter decomposition across multiple spatial scales in stream networks
Oecologia, 2009
Spatial scale is a critical consideration for understanding ecological patterns and controls of ecological processes, yet very little is known about how rates of fundamental ecosystem processes vary across spatial scales. We assessed litter decomposition in stream networks whose inherent hierarchical nature makes them a suitable model system to evaluate variation in decay rates across multiple spatial scales. Our hypotheses were (1) that increasing spatial extent adds signiWcant variability at each hierarchical level, and (2) that stream size is an important source of variability among streams. To test these hypotheses we let litter decompose in four riZes in each of twelve 3rd-order streams evenly distributed across four 4th-order watersheds, and in a second experiment determined variation in decomposition rate along a stream-size gradient ranging from orders 1 to 4. DiVerences in decay rates between coarse-mesh and Wne-mesh litter bags accounted for much of the overall variability in the data sets, and were remarkably consistent across spatial scales and stream sizes. In particular, variation across watersheds was minor. DiVerences among streams and among riZes were statistically signiWcant, though relatively small, leaving most of the total variance (51%) statistically unexplained. This result suggests that variability was generated mainly within riZes, decreasing successively with increasing scale. A broad range of physical and chemical attributes measured at the study sites explained little of the variance in decomposition rate. This, together with the strong mesh-size eVect and greater variability among coarse-mesh bags, suggests that detritivores account, at least partly, for the unexplained variance. These Wndings contrast with the widespread perception that variability of ecosystem characteristics, including process rates, invariably increases (1) with spatial extent and (2), in stream networks, when analyses encompass headwaters of various size. An important practical implication is that natural variability need not compromise litter decomposition assays as a means of assessing functional ecosystem integrity.
Input of litter in deforested and forested areas of a tropical headstream
Brazilian Journal of Biology, 2010
Riparian vegetation is the main source of leaves and the main energy source for low order streams. Therefore, changes in its composition affect the structure and processes in streams. We studied the contribution of the riparian vegetation by analysing the annual input of litter in deforested and forested areas of a tropical stream. The lateral, vertical (aerial) and horizontal (drift) litter inputs were analysed separately. The lateral input differed significantly between the two areas and included mostly fallen dry leaves. The vertical input, represented mainly by fallen dry leaves, occurred only in the forested area. The drift transport of litter was not significantly different between the deforested and forested areas and the input was composed mostly by CPOM. The removal of the native forest was clearly reflected in the low contribution of leaf litter in the deforested area.
Leaf litter processing in low order streams
2006
Forests produce a large amount of detritus, that inevitably end up in streams, subsidizing aquatic systems with organic matter and nutrients. Here we review some of the research carried out at the University of Coimbra with the objective of getting a better understanding of the breakdown process of these materials and its incorporation to secondary production. Litter-fall in deciduous forests in Central Portugal can reach up to 750 g AFDM of leaves m -2 yr -1 , with 73% of the litter produced between October and December. In several retention experiments, we measured a 90% leaf retention in low order (1 st -4 th ) streams within 15 -70 m, and a standing stock of up to 450 g AFDM m -2 . The amount of nutrients in the water and the plant physical and chemical defenses can be an indicator of the rate at which plant material is incorporated into secondary production or exported as dissolved and fine particles of organic matter. Respiration rates of decomposing leaves incubated with fungicides were severely reduced, supporting the idea that fungi are very important agents in litter breakdown. The fungi group known as aquatic hyphomycetes are capable of producing enzymes able to cause leaf maceration, and by 2 to 3 weeks, up to 15 % of the decomposing leaf biomass corresponds to fungi. Shredder invertebrates are also biological agents involved in litter breakdown. Given their densities and feeding rates, we measured consumption rates of 12 -54 g of leaves m -2 yr -1 in a stream in Central Portugal, corresponding to 2 to 9 times the litter standing stock. Feeding rates were high in nutrient rich leaves and low in chemical and physically protected leaves with low nutrient content. According to several experiments, fungal colonization facilitates the access of invertebrates to the energy trapped in deciduous leaves in streams. Some invertebrates have strategies to cope with low quality food (leaves with low microbial biomass or high chemical defenses). Those include high mobility, small size, compartmentalized digestion in the gut, presence of endosymbionts, and the capability to decrease respiration rates. The relative importance of fungi and invertebrates in the incorporation of plant litter material into secondary production varies across rivers and biomes. Shredder invertebrates seem to play a key role in litter breakdown in headwaters, but their importance appears to decrease downstream. In the same way, some systems where leaves are hard or protected, shredder invertebrates may be less abundant and the energy may be mainly recovered from litter by fungi. Eucalyptus plantations are systems with low diversity of invertebrates and aquatic hyphomycetes. Streams running through eucalyptus plantations seem therefore ideal to experimentally investigate relationships between structural parameters (biodiversity) and function. Finally, our research has been extended to other climatic areas including the Mediterranean and tropical streams. We reported a wide variety of situation in those systems. A general rule applying to all of them is that if leaf litter is abundant and high quality, the incorporation of energy into detrital food webs can be processed very quickly. However, if leaves are well protected and nutrients in the water are low, processing rates are equally very low, independently of the ambient temperatures.
The high plant richness in riparian zones of tropical forest streams and the relationship with an input of organic matter in these streams are not well understood. In this study, we assessed (i) the annual dynamics of inputs of coarse particulate organic matter (CPOM) in a tropical stream; and (ii) the relationship of species richness on riparian vegetation biomass. The fluxes and stock of CPOM inputs (vertical-VI = 512, horizontal-HI = 1912, and terrestrial-TI = 383 g/m 2 /year) and the benthic stock (BS = 67 g/m 2 /month) were separated into reproductive parts, vegetative parts and unidentified material. Leaves that entered the stream were identified and found to constitute 64 morphospecies. A positive relationship between species richness and litterfall was detected. The dynamics of CPOM were strongly influenced by rainfall and seasonal events, such as strong winds at the end of the dry season. Leaves contributed most to CPOM dynamics; leaf input was more intense at the end of the dry season (hydric stress) and the start of the rainy season (mechanical removal). Our study show an increase of litter input of CPOM by plant diversity throughout the year. Each riparian plant species contributes uniquely to the availability of energy resources, thus highlighting the importance of plant conservation for maintaining tropical streams functioning.
Leaf-litter breakdown in tropical streams: is variability the norm?
Freshwater Science, 2015
Many forested headwater streams are heterotrophic ecosystems in which allochthonous inputs of plant litter are a major source of energy. Leaves of riparian vegetation entering the stream are broken down by a combination of biotic and abiotic processes and, in most temperate and boreal streams, provide food and habitat for