Organic Matter Processing and Detrital Food Webs III Posters
Presiding: E Marti, Centre d'Estudis Avancats de Blanes (CSIC); C Hoagstrom, South Dakota State University
NB33I-01 1330h
The Source of Bacteria Involved in the Break-Down of Gammarus Pulex Faecal Pellets Using Image Analysis
Bacteria survive passage through the gut of aquatic animals and are implicated in the break-down of POM (such as faecal pellets) in aquatic systems. There is evidence that bacteria that survive gut passage are the cause of the initial break-down of faecal pellets, rather than colonisation by bacteria from the environment. Gammarus is the dominant shredder in lowland permeable catchments ("chalk streams") in England and feeds on allochthonous detritus such as fallen leaves. Gammarus faecal pellets could form important pathways for transfer of organic matter in chalk streams. We incubated Gammarus faecal pellets for 80 days in stream water using combinations of treatments (autoclaving the stream water or pellets; fresh non-autoclaved stream water or pellets; reducing bacterial activity using Gentamicin; combinations of these treatments) to assess the role of surviving and colonising bacteria on the break-down process. Break-down was measured using image analysis. Results show that treatments with fresh pellets show much higher levels of break-down than fully autoclaved controls, treatments with fresh stream water but autoclaved pellets, or treatments with Gentamicin. Bacteria surviving gut passage therefore seem to play a greater role in faecal pellet break-down than those colonising from the environment.
NB33I-02 1330h
Macroinvertebrates Associated With Emergent Macrophyte Decomposition in a Constructed Wetland.
This study took place at the San Jacinto constructed wetland in California. Wetland water is supplied to irrigators in this cooperative venture between Reclamation and the Eastern Municipal Water District. One of the problems at this highly productive site is that plant litter accumulates to where it needs to be managed by taking the wetland off-line, thus impacting O&M costs and water delivery schedules for extended periods. Information on decomposition rates and conditions needed to encourage invertebrate decomposers was required to improve wetland reliability and decrease biomass management costs. Standing dead culms of bulrush (Schoenoplectus) were collected and air-dried to constant weight. Twenty-gram culm packs were placed in the wetland and then collected at two month intervals. Comparisons between fine-mesh and coarse-mesh packs demonstrated that exclusion of aquatic invertebrates decreased processing. This was also demonstrated in laboratory studies. It also appeared that culm pack decomposition rate varied with the macroinvertebrate community, and that community distribution was influenced by water quality. Study results confirm the importance of vegetation management through water management and wetland design. Maintaining healthy, sustainable ecosystems will help to encourage natural decomposition processes and maintain better water quality.
NB33I-03 1330h
Diversion dam reduces decomposition, fungal biomass, and macroinvertebrate abundance and diversity: Implications for dam removal
Dam decommissioning projects are rarely accompanied by adequate baseline data needed to test if the effects of dams are reversible. Although the effects of dams on aquatic species have been well-documented, there are few studies that document the effects of dams on ecosystem processes. In this study we examine how in-stream leaf litter processing rates and associated fungal and macroinvertebrate populations are affected by a dam in Fossil Creek, Arizona, which will be decommissioned in 2005. We found significantly faster decomposition rates above the dam accompanied by higher fungal biomass, invertebrate abundances and invertebrate diversity compared to below the dam. We predict that return of full flows will increase decomposition, fungal biomass, and secondary productivity in areas where flow is currently reduced. This study shows how diversion dams can inhibit ecosystem processes and provides data for testing the restoration potential of dam decommissioning on decomposition and decomposer communities.
NB33I-04 1330h
Effects of Tropical Depressions Frances, Ivan, and Jeanne on Wood Input to Southern Appalachian Streams
The tracks of tropical depressions (TDs) Frances, Ivan, and Jeanne during September 2004 resulted in 40 cm of precipitation, wind speeds of 48-64 km/h, and numerous downed trees in the Coweeta basin of the southern Appalachians. We collected fallen wood from a net canopy covering a headwater stream (C55) and compared these amounts to wood inputs measured from 1997 to 2004. Wood input during the 3 TDs made up 70% of the total annual input of wood (292 g AFDM/m2) to C55 during 2004 and was the largest monthly input of wood in 7 years. Wood input during the 3 TDs accounted for 29% of wood inputs in the past 7 years and 4% of initial standing crop of wood in this stream. Large wood (>10 cm diameter) made up 41% of total wood inputs during the 3 storms. Using mean bankfull widths and total stream lengths previously calculated for Coweeta, 46.5 metric tons of wood fell into 15.9 ha of stream area within the basin as a result of the TDs. This is 5 times the mean annual input of wood measured previously. These data demonstrate the large temporal variation associated with wood inputs to streams and the importance of long-term measurements.
NB33I-05 1330h
Effects of Manipulating Leaf Inputs on the Biomass and Communities of Aquatic Hyphomycetes in a Southern Appalachian Stream
We are examining effects of manipulating leaf inputs on the fungi in a headwater Appalachian stream. Leaves had been excluded from the treatment stream for eight years at the beginning of the study. In the autumn of the first two years, rapidly decomposing leaves of three tree species (dogwood, yellow poplar, sweet gum) were added at the rate that leaves naturally fell into a reference stream nearby. In each of the following two autumns, leaves that decompose slowly (rhododendron, red oak, white pine) were added to the stream. Fungal biomass (ergosterol concentrations) associated with leaves increased after leaf input and exhibited similar patterns in both streams in all years. Conidia in transport in the treatment stream peaked at higher concentrations (3 to 15 times) than observed in the reference stream during April-May in the first year and February in the second year following addition of rapidly decomposing leaves. After addition of slowly decomposing leaves, conidia concentrations exhibited broader, later maxima than in the first two years or in the reference stream. Species richness of fungi was similar in both streams during leaf additions (average of 16-17 species per sampling date). However, relative abundances and ranking of dominant species were altered.
NB33I-06 1330h
The Influence of Shredder Feeding on Fungal Activity in a Nutrient-Enriched Stream and an Unaltered Stream
The effect of shredder feeding on aquatic hyphomycete communities associated with submerged leaves was studied in two southern Appalachian headwater streams in North Carolina. Coarse and fine mesh litter bags containing red maple (Acer rubrum) leaves were placed in the nutrient-enriched stream and in the reference stream and were retrieved monthly. Both shredder feeding and nutrient enrichment enhanced breakdown rates. The breakdown rates of leaves in coarse mesh bags in the reference stream (k = 0.0275) and fine mesh bags in the nutrient enriched stream (k = 0.0272) were not significantly different, suggesting that the shredding effect on litter breakdown was offset by higher fungal activity as a result of nutrient enrichment. Fungal sporulation rates and biomass (based on ergosterol concentrations) were higher in the nutrient enriched than in the reference stream, but neither fungal biomass nor sporulation rate was affected by shredder feeding. Species richness was higher in the nutrient-enriched than in the reference stream. The enrichment with nutrients altered fungal community composition more than shredder feeding.
NB33I-07 1330h
Influence of Initial Leaf Pack Size on Estimates of Breakdown Rates in Streams
Experiments to determine the influence of leaf pack size on estimates of breakdown rates were conducted in Stony Run, a moderately hardwater stream in central Pennsylvania draining mature second-growth forest. We deployed 5-mm mesh bags containing different initial amounts (2, 5, 10, 20, and 50 g) of white oak leaves at 3 sites in Stony Run during October 2004. Bags have been retrieved monthly and were processed to determine ash-free dry mass remaining and abundance of shredder-detritivores in the bags. Breakdown rates varied from 0.018 d-1 in 50 g bags to 0.015 d-1 in 2 g bags and were strongly correlated with initial weight of leaf litter (log10 initial leaf mass vs. breakdown rate r = 0.99). Total invertebrate abundance was initially higher in heavier leaf bags, and proportion of shredders increased as leaf mass declined throughout the study. Shredder abundance was positively correlated with leaf pack size (r = 0.76) and breakdown rate (r = 0.82), which indicates that shredders were more important in determining breakdown rates than mechanical fragmentation or microbial activity. These results suggest that models of stream organic matter dynamics should incorporate distribution of natural leaf packs and higher breakdown rates associated with densely packed leaves.
NB33I-08 1330h
The Effects of Land-use on Seston Size in Southern Appalachian Streams
To assess effects of land-use on stream seston, we took samples from nine streams draining three land-use types: forested (reference), agricultural, and residential. Samples were collected in mid-August and mid-November. We determined the distribution of particle sizes (ultrafine (0.45-25 Îœm), very fine (25-45 Îœm), fine (45-100 Îœm), small (100-250 Îœm), and medium large (250-1000 Îœm)), % organic, and chlorophyll-a content. Larger particles were found in forested streams and smaller particles were found in residential streams. Chlorophyll-a content was higher in residential and agricultural streams. The larger particles in forested streams were probably due to biological fragmentation of leaves whereas the smaller particles in residential streams were most likely the result of soil erosion. The chlorophyll-a content of seston was related to the openness of the canopy over the sites.
NB33I-09 1330h
Leaf Litter Composition and Benthic Macroinvertebrate Community Assemblages in Northern Forested Watersheds With Differing Land Use Histories
In northern forested ecosystems, the autumnal leaf fall constitutes the majority of carbon and nitrogen that enters headwater streams annually. This study compared small upland watersheds located in two types of land use categories in the Adirondack Park; State Forest Preserve Lands, and lands that have been logged during the past 25 years. Riparian litter quality and biomass amounts were estimated for each stream. Leaf Litter quality was determined from the results of previous studies on individual species of litter. In-stream leaf packs were also sampled to assess invertebrate community assemblages, and leaf pack species composition. Leaf packs in managed streams were composed mainly of high quality litter, although leaf packs in Preserve streams had a higher abundance of macroinvertebrates. These data may have many important implications for ecosystem energetics as it relates to land use practices.
NB33I-10 1330h
Allochthonous Matter Input in Five Headwater Streams in Southwestern Colombia
In order to determine the interactions between riparian vegetation and the stream environment in relation to the provision and seasonality of allochthonous energy, a study was done measuring the amount of litter inputs in five streams at mid altitude in southwestern Colombia during one year. Direct and lateral litter traps were placed in a 100m reach of each stream. Total amount of litter fall ranged from 1406 to 2812 g-m-2 year-1. Leaves were the most important component of the litter representing between 56 to 72% of direct and between 68 to 81% of lateral inputs. Seasonality of litter fall was minimal and only in one stream direct input was negatively correlated with rainfall (r=-0.62; p=0.033). According to these results, low-order streams in middle altitude in Colombia receive one of the highest amounts of litter fall reported so far. This supply is constant throughout the year providing a continuous source of food and substrate for the stream environment. As in temperate streams litterfall in the Andean zone is an important link between streams and the riparian environment. The higher amount recorded and the constant supply demonstrate that deforestation of riparian forests may be more negative for the streams in tropical areas.
NB33I-11 1330h
Stable Isotopic Relationships among Biofilm, Algae, and Dissolved Organic Carbon in two Ozark Streams: Spatial and Temporal Considerations
The identification of carbon (C) sources fueling microorganisms is critical to our understanding of stream biogeochemistry. Biofilm, filamentous algae, and dissolved organic carbon (DOC) samples were collected from two contrasting streams to discern biofilm microbial C sources. Samples were collected from multiple sites, representing a gradient in flow, and over diurnal periods to study the variation in the stable isotopic composition of biofilm in relation to DOC and algae. The stable isotopic composition of biofilm phospholipid fatty acids (Δ13CBPLFA) was used to distinguish between heterotrophs and autotrophs. Bulk biofilm and algae were typically enriched (2-6 ‰) in pools relative to fast flowing reaches. The Δ13C of bulk biofilm and algae also changed diurnally with more enriched values occurring in late afternoon in both streams. Diurnal change in Δ13CCDOC, however, was only detected in the nutrient-poor stream. The Δ13CBPLFA data from the nutrient-poor stream suggest heterotrophs follow variations in algae and DOC, and were more enriched in 13C relative to both algae and DOC. This suggests heterotrophs may utilize exudates from the algae or a specific component of the DOC. The Δ13CBPLFA from the nutrient-rich stream were far less dynamic suggesting less preferential use of a specific component of the DOC pool.
NB33I-12 1330h
Relative Contributions of Leaf-associated Microorganisms to Leaf Litter Breakdown in a Nutrient-enriched Headwater Stream
Litter decomposition in streams occurs as a function of microbial and invertebrate processing, as well as abiotic factors. Abiotic factors, such as streamwater nutrient concentrations, may change the relative importance of groups of microorganisms, as well as invertebrates, to leaf breakdown. We plan to quantify the relative contributions of bacteria, fungi, and invertebrate processing on decaying leaves in a reference and treatment stream (experimentally enriched with N & P for 4.5 yrs) at the Coweeta Long Term Ecological Research site in North Carolina, USA. Leaf packs of maple or rhododendron leaves were periodically retrieved to determine decay rates. Microbial activity was measured as respiration, fungal biomass was determined by measuring ergosterol concentration, and bacterial biomass was determined by epifluorescence microscopy. Breakdown rates were dramatically faster in the nutrient enriched stream than the reference stream, associated with greater microbial activity and presumably, invertebrate feeding. Based on whole-system response by microorganisms, we predict that nutrient enrichment will lead to greater contributions of fungi, relative to bacteria, to leaf breakdown. Our results show that enrichment can fundamentally alter the rate of organic matter breakdown in streams, and will test whether enrichment also changes the relative roles of groups of organisms contributing to breakdown processes.
NB33I-13 1330h
Effects of Crayfish on Quality of Fine Particulate Organic Matter
The origin and ontogeny of detritus often determines its bioavailability. Crayfish shred and consume detrital organic matter, influencing fine particulate organic matter (FPOM) availability, composition and quality. Given consumption of FPOM by many invertebrates, crayfish can indirectly affect these organisms by altering FPOM bioavailability through organic matter fragmentation, biofilm disturbance, and defecation. These effects may or may not vary among coarse particulate organic matter (CPOM) from different leaf species. To assess crayfish effects on FPOM quality, crayfish were fed stream-conditioned maple or oak leaves in hanging 1-mm mesh-bottom baskets in aquaria. After 12 h, crayfish and remaining leaves were removed. FPOM fragments that fell through the mesh were vacuum filtered and analyzed for percent organic matter, C:N ratio, and bacterial abundance. The same analyses were conducted on crayfish feces collected using finger cots encasing crayfish abdomens. C:N ratios did not differ between feces and maple leaf CPOM, but were lower in FPOM produced through fragmentation and disturbance (P = 0.023). Overall, crayfish alter the ontogeny of detritus, which may, in turn, affect stream FPOM dynamics.
NB33I-14 1330h
Influence of Leaf Chemical Composition on Bacterial and Fungal Colonization During Leaf Litter Decomposition in a Venezuelan stream
We studied bacterial and fungal colonization during decomposition of leaf litter differing in chemical composition in a small intermittent stream of northwestern Venezuela. Litter bags containing leaves of Tabebuia roseae, Ficus sp, Hura crepitans and Anacardium excelsum were incubated during 42 days in the stream. Six bags were retrieved after 2, 7, 14, 21, 28, 35 and 42 days and the mass loss was registered. Leaves were initially analyzed for N, P, Lignin and Polyphenols in order to assess the chemical composition of each species. Conidia of aquatic hyphomycetes were identified and quantified after in vitro incubation of leaves with filtered stream water. Bacteria were counted and identified using an epifluorescence microscope. The species H. crepitans and Ficus sp showed higher decomposition rates than T. roseae and A. excelsum. Higher conidia production was observed in Anacardium leaves, while bacterial density and biomass resulted higher in Hura leaves. Our results suggest that chemical composition of leaves differentially affected to bacteria and aquatic hyphomicetes colonization. Bacteria colonized earlier than fungi during leaf litter decomposition process.
NB33I-15 1330h
Changes in Microbial Extracellular Enzyme Activity Associated with Decreasing Organic Matter Particle Size in a Louisiana Cypress Swamp
Microbial extracellular enzymes are vital to the decomposition of fine particulate organic matter (FPOM) in aquatic systems. However, little is known about variations in the activity of these enzymes with decreasing FPOM size, and even less is known about the importance of these enzymes in the decomposition of FPOM in wetland sediments. Three sediment samples were collected from a Louisiana cypress swamp and sieved into five size ranges, consisting of course particulate organic matter (>1 mm), and four different sizes of FPOM: 0.5-1mm, 0.25-0.5mm, 0.125-0.25mm, and 0.063-0.125mm. For each size range, we assayed the activities of six enzymes involved in lignocellulose decomposition. Activities of beta-glucosidase, beta-xylosidase, cellobiohydrolase, and beta-N-acetylglucosaminidase were strongly correlated with each other, and the activities of all four hydrolytic enzymes began to decrease in activity on FPOM less than 0.5mm. Peroxidase activity was generally low, but peaked on 0.125-0.25mm particles. Phenol oxidase activity was not detected in any samples, regardless of particle size. These results show that changes in microbial enzyme activity occur as FPOM decreases in size, particularly on particles below a 0.25-0.5mm threshold. These changes may reflect differences in both the microbial community and the nature of the FPOM.
NB33I-16 1330h
Effect of Macroinvertebrate Functional Diversity on Leaf Decomposition in a Laboratory Experiment
Biodiversity on earth is decreasing, yet still little is known of the effects of this loss on ecosystem functioning. The majority of studies dealing with species diversity and ecosystem functioning found a positive relationship. Different species may have similar functions in an ecosystem and can be clustered in functional groups. Based on their adaptations for food acquisition, macroinvertebrates are divided in different functional feeding groups. We performed a 12 days lasting laboratory experiment in which we studied the decomposition of poplar leaves under different combinations of three functional feeding groups (shredders, collector-filterers, grazers). As test-organisms were used: Gammarus pulex and Asellus aquaticus as shredders, Bythinia tentaculata and Planorbis planorbis as grazers, and Dreissena polymorpha and Hydropsyche angustipennis as collector-filterers. The results of our experiment show that all three functional groups alone contributed significantly to the decomposition of the poplar leaves, with the greatest decomposition rate by shredders. The contribution of the collector-filterers is due to leaf use for case building by H. angustipennis. Decomposition by shredders in combination with grazers or collectors or both grazers and collectors is not significantly different from decomposition by shredders alone. Therefore, there seems no relationship between functional feeding-group diversity and rate of decomposition.
NB33I-17 1330h
Influence of Acid Precipitation and Liming on Leaf Breakdown in Virginia Streams
Acid precipitation has long been a problem in the eastern United States. We evaluated the impact of acid precipitation and the efficacy of liming on leaf breakdown in 4 streams in western Virginia. These streams have been chronically acidic and each stream has been limed for nearly a decade. At 10 sites distributed above and below liming stations on each stream and in 2 additional sites in a naturally buffered stream we incubated 18 packs containing 8g of Chestnut Oak leaves. Packs were collected in triplicate from each site at monthly intervals from November 2003 to May 2004. Mean pH ranged from 4.9 upstream of liming stations to 6.8 in the naturally buffered stream. Liming raised pH of the streams by 0.1-0.6 units. Leaf breakdown rates ranged from 0.0015 day-1 upstream of liming stations to 0.0058 day-1 in the naturally buffered stream. Breakdown rate was generally faster downstream of liming sites and differences in breakdown rate among sites was largely explained by variation in pH (r = 0.67, p = 0.001). Slower breakdown was at least partly due to reduced microbial respiration on leaves in acidic sites. Overall, liming was moderately effective in restoring leaf breakdown in acidified streams.
NB33I-18 1330h
Patterns of Metabolism and Organic Matter Resource Availability Along a Tallgrass Prairie Stream Continuum
Stream metabolism and organic matter resources were quantified in a grassy headwater, shrubby mid-reach, and forested lower reach of a tallgrass prairie stream. Reach-level metabolism was estimated seasonally using the single station method and monthly benthic samples were used to estimate organic matter resources during 2003-2004. Average net metabolism for the grassy headwater, shrubby mid-reach, and gallery forest was -0.008gO2/m2/d, -0.028gO2/m2/d, and -0.026gO2/m2/d, respectively. Average coarse particulate organic material (CPOM, >1mm) totals were 69gAFDM/m2 in the grassy headwaters, 161g AFDM/m2 in the shrubby mid-reaches, and 107gAFDM/m2 in the gallery forest. Within CPOM, miscellaneous unidentified materials, grass, and aquatic macrophytes dominated the grassy headwaters (39%, 27%, and 14%, respectively), while leaves (57%) were dominant in the shrubby mid-reaches, and leaves (48%) and wood (30%) were co-dominant in the gallery forest. Average fine particulate organic matter (<1mm>250Îœm) standing stocks ranged from 56gAFDM/m2 in the headwaters to 17gAFDM/m2 in the gallery forest. Very fine particulate organic matter (<250Îœm) ranged from 404gAFDM/m2 in the grassy headwaters to 217gAFDM/m2 in the gallery forest. As predicted by the River Continuum Concept, we found patterns of changing energy resources along this prairie stream continuum, but they differed from the specific RCC predictions for streams with forested headwaters.
NB33I-19 1330h
Comparison of Leaf Breakdown for Native and Non-native Riparian Species in Streams Draining Urban, Agricultural, and Forested Land Cover.
Organic matter breakdown rates in streams vary among riparian tree species and are dependent on a variety of in-stream biological, chemical, and physical factors. These factors and the composition and distribution of riparian vegetation are changed by anthropogenic modification of the landscape. This may result in altered energy flow through stream ecosystems that is reflected in changes in organic matter input and breakdown. The goal of this study was to compare leaf breakdown rates between a native (box elder, Acer negundo) and non-native (weeping willow, Salix babylonica) species among three land cover categories: urban, agricultural, and forested. We conducted this study over 14 weeks in 13 streams near Roanoke, Virginia. Box elder occurs naturally along disturbed riparian corridors in this region, while weeping willow has been actively planted for its aesthetic value. Our results indicate weeping willow breakdown rates were faster than box elder across all land cover categories. Breakdown rates for both species were slowest in the urban streams, intermediate in agricultural streams, and fastest in forested streams.
NB33I-20 1330h
Annual Production of Decomposer Fungi Associated With Standing-Dead Litter of Typha angustifolia
Microbial decomposition of standing-dead plant litter is an important process in wetlands dominated by emergent macrophytes. We determined the annual fungal biomass (ergosterol) and production (14C-acetate incorporation) associated with decaying standing litter (leaves and shoots) of the emergent macrophyte Typha angustifolia in small lake littoral wetland in southeastern Michigan. Mean annual detrital mass of standing-dead leaf and shoot litter was 656±238 g/m2 (range 284-873) and 1184±280 g/m2 (range 522-1525), respectively, during study period. Mean annual fungal biomass associated with decaying standing litter was 46 and 15 g/m2 for leaves and shoots, respectively. Annual fungal biomass production associated with leaves and shoots was 168 and 78 g/m2, respectively, with maximum production /m2 occurring during the summer season. These production estimates account for diel periodicity in water availability and the consequent periodicity in microbial activities that are characteristic of the standing litter environment. A partial organic matter budget constructed for this littoral wetland indicates that 9.4% of the annual aboveground production of T. angustifolia went into the production of fungal biomass. These results provide additional evidence indicating considerable carbon flow from emergent plant matter to fungal decomposers while in the standing-decay phase.