Ash-free Weight Research Articles

The seasonal response of metabolic rate to projected climate change scenarios in aquatic amphipods

The responses of organisms to climate change are mediated primarily by its impact on their metabolic rates, which, in turn, drive various biological and ecological processes. Although there have been numerous seminal studies on the sensitivity of metabolic rate to temperature, little is empirically known about how this rate responds to seasonal temperature ranges and beyond under conservative IPCC climate change scenarios. Here, we measured the SMR of the aquatic amphipod, Gammarus insensibilis, which served as our subject species, with body masses ranging from 0.20 to 7.74 mg ash free weight. We assessed the response of the SMR across nine temperature levels ranging from 12 to 30.2 °C. These temperatures match seasonal temperature norms, with an incremental increase of 0.6–1.2 °C above each seasonal baseline, as projected for the years 2040 and 2100 under the modest climate change scenarios. Overall, our findings showed that the effect of temperature on SMR varies with body mass, as indicated by a negative size-temperature interaction, with larger conspecifics exhibiting less sensitivity to temperature changes than smaller ones. From the cold to warm season, the SMR increased by an average of 14% °C−1, with increases of 18.4% °C−1 in smaller individuals and 11.4% °C−1 in larger ones. The SMR of smaller individuals peaked at a 0.6 °C increase from the current summer baseline (15.08% °C−1, Q10 = 4.2), while in larger ones it peaked with a 1.2 °C increase beyond autumn temperatures (14.9% °C−1, Q10 = 3.9). However, at temperatures reflecting global warming that exceed summer temperatures, the SMR of larger individuals levelled off, while that of smaller ones continued to increase. Overall, our findings suggest that smaller-sized individuals have a broader thermal window for SMR performance, while the SMR of larger-sized ones will become increasingly constrained at summer temperatures as those summer temperatures become hotter.

Decomposition of green manure and nutrients release in Subarctic, Kola Peninsula, Russia

In the field experiment, the intensity of decomposition and release of nutrients was studied for six types of plant residues – leaves, panicles and straw of oats (Avena sativa), as well as whole plants of lupine (Lupinus angustifolius), phacelia (Phacelia tanacetifolia) and vetch (Vicia sativa) in the arable horizon of Anthrosols on the Kola Peninsula. Samples in mesh nylon bags were sampled after 8, 12 and 24 months of exposure in soil. The loss of weight, the content of Corg and Norg, as well as ash elements – Si, Al, Fe, K, Ca, Mg, P, S and Mn were determined in all plant residue samples. As the results showed, despite the low temperatures, the decomposition of green manure in soil occurred with a high intensity, comparable to the southern chernozem zone: after a year of exposure in the soil, plant residues lost from 47% (oat straw) to 75% (lupine) of their initial ash-free weight. After 2 years, weight loss reached 68% in oat straw and 90% in lupine. The distribution of losses of Corg, Norg, and P between the types of plant residues and decomposition periods correlated significantly (at p≤0.01) with the distribution of weight losses. Changes in the content of other ash elements did not depend on weight loss: depending on the type of material and the stage of decomposition, the samples could not only lose them (K – by all plant residues; Mn – by lupine; S, Ca and Mg – by all plant residues, except straw and oat panicles), but also accumulate them in quantities exceeding the initial ones (Fe – by all species, Mn – by all species except lupine; Ca and Mg – by straw and oat panicles) at certain periods. The accumulation of elements above initial level means that the transformed plant residues can accumulate additional amounts of elements from the soil solution, while the irregular alternation of increases and decreases in Ca, Mg, S, Fe and Mn indicates the reversible nature of the process. Due to the significant differences between the types of green manure in terms of chemical composition, rate and dynamics of decomposition and release of nutrients, their use provides great opportunities for managing soil fertility and the intensity of elements cycling in agrocenoses through the species selection.

Model Exploration and Application of Near-Infrared Spectroscopy for Species Separation and Quantification during Mixed Litter Decomposition in Subtropical Forests of China

Litter of different species coexists in the natural ecosystem and may induce non-additive effects during decomposition. Identifying and quantifying the origins of species in litter mixtures is essential for evaluating the responses of each component species when mixed with co-occurring species and then unraveling the underlying mechanism of the mixing effects of litter decomposition. Here, we used near-infrared spectroscopy (NIRS) to predict the species composition and proportions of four-tree species foliage mixtures in association with litter crude ash and litter decomposition time. To simulate the whole mixed litter decomposition process in situ, a controlled mixture of four tree species litter leaves consisting of 15 tree species combinations and 193 artificial mixed-species samples were created for model development and verification using undecomposed pure tree species and decomposed litter of single tree species over one year. Two series of NIRS models were developed with the original mass and ash-free weight as reference values. The results showed that these NIRS models could provide an accurate prediction for the percentage of the component species from in the litter leaf mixture’s composition. The predictive ability of the near-infrared spectroscopy model declined marginally with the prolonged litter decomposition time. Furthermore, the model with ash-free litter mass as a reference exhibited a higher coefficient of determination (R2) and a lower standard error of prediction (RMSECV). Thus, our results demonstrate that NIRS presents great potential for not only predicting the organic composition and proportion in multi-species mixed samples in static conditions, but also for samples in dynamic conditions (i.e., during the litter decomposition process), which could facilitate evaluation of the species-specific responses and impacts on the interspecific interactions of co-occurring species in high-biodiversity communities.

Fine root decomposition in tropical dry evergreen and dry deciduous forests in Thailand

Dry evergreen forest (DEF) and dry deciduous dipterocarp forest (DDF) are major forest types extensively distributed in northeastern Thailand, exhibiting different nutrient cycling properties. This study aims to improve our understanding on the pattern of mass loss and nitrogen release from two categories of roots (fine, <2 mm and small, 2–5 mm) of Hopea ferrea at DEF and fine roots of mixed trees and dwarf bamboo (Arundinaria pusilla) at DDF sites. Decomposition experiment was performed for more than 12 months using buried litter bag technique. Initial chemistry was significantly different among the four root litters; fine root of H. ferrea exhibited a low ratios of C:N and acid-insoluble:N. The fine root of dwarf bamboo was characterized by high contents of total carbohydrate and ash. Decomposition rate constants (year−1) of ash-free weight remaining were 1.27 and 0.55 for fine and small roots of H. ferrea, and 0.73 and 0.66 for fine root of mixed trees and dwarf bamboo, respectively. At the end of the experiment, the N concentration in fine and small roots of H. ferrea increased to 1.5 times the initial concentration. Whereas, N mass of dwarf bamboo decreased during the experiment. This suggests a different pattern of root decomposition and N release in two forest ecosystems. Generally, the fine root decomposition was faster in the DEF than in the DDF. The role of initial litter chemistry was more pronounced than the climatic seasonality on the belowground decomposition pattern in our study.

Decomposition of fine roots and α-cellulose in a short rotation willow (Salix spp.) plantation on abandoned agricultural land

Decomposition of fine roots (&lt;1 mm in diameter) of the clones of Salix viminalis, S. dasyclados and α-cellulose sheets (50 x 10 x 1 mm) was studied in a 6-years old Salix spp. plantation established on abandoned agricultural land in Estonia. The substrates were incubated in litterbags (mesh size 0.14 mm) in 5–10 cm topsoil, in non-fertilised plots for one year. Changes in the ash-free weight of the fine roots were best described by negative exponential models (S. viminalis R = 0.98, S. dasyclados R = 0.96), and by a linear model for α-cellulose (R = 0.63). The sheets of α-cellulose decomposed roughly twice as rapidly as the fine roots (S. viminalis k = 0.325, S. dasyclados k = 0.165). The remaining (of the initial) ash-free weights of the fine roots were 73.3 ± 0.8% (mean ± SE) and 85.8 ± 2.2% respectively, and of the α-cellulose 35.9 ± 8.5%, in the end of the one year of decomposition. The amount of acid detergent (AD) lignin in the fine-roots of S. viminalis increased significantly and did not change in S. dasyclados, suggesting higher activity of microbial decomposers in the first substrate. Of the studied quality parameters, the AD lignin was the major factor determining the different rate of decomposition of the fine roots of S. viminalis and S. dasyclados. Nitrogen was recycled in the fine root sub-system in both Salix species. This knowledge can be applied in the management of Salix plantations, aimed at bioenergy production.222

Decomposition and nutrient release from leaf litter of Eucalyptus globulus grown under different water and nutrient regimes

Leaf litter from stands of Eucalyptus globulus Labill., of varying chemical composition was used to study decomposition rates and the release of nutrients (N, P, S, K, Ca, Mg). Leaf litter from control plots, which received no additional fertiliser or water (C), from fertilised plots (F), from irrigated plots (I) and from irrigated and fertilised plots (IL and ILN) was used. IL was collected during June–July and ILN during September. The C, F and I contained lower N and P than the IL and ILN, and had also a lower lignin content. Litterbags were used to study decomposition during a period of 643 days. The remaining ash free weight after 643 days of incubation ranged from 52.8% in C leaf litter to 47.9% in ILN leaf litter. The decomposition rates of leaf litter were 0.37 per year for C and 0.42 per year for ILN. Decomposition rates and weight losses were not significantly different among leaf litters, irrespective of different N and P concentrations, C/N ratios and lignin/N ratios. The concentration of N, S, and Ca in all substrates studied were higher at the end of the incubation period than at the beginning whereas the concentrations of K and Mg were lower. P concentration was lower at the end than at the beginning of the experiment, except for C leaf litter. The increase in N concentration was inversely correlated to its concentration in the original leaf litter. During the early decomposition stages (133 days), release of N, P and Ca was positively correlated to their initial concentration. Except for S and Ca, the amount of N, P, Mg and K remaining at the end of the experiment was similar to that determined after the early decomposition stages. The improvement of leaf litter quality through fertiliser application did not increase decomposition rate, but the release of N and P was enhanced.

Assessment of errors in nutrient analyses of roots

Errors in nutrient analyses of roots may arise from soil adhering to roots, the method of root separation from soil and storage of root samples. Experiments were conducted on fine roots of Eucalyptus nitens from a clay soil to establish a method for estimating true concentrations of nitrogen (N), phosphorus (P) and potassium (K) in root samples (i.e. unbiased by the soil adhering to roots), and to test the adequacy of measurements of ash residues of root samples for estimating the quantity of soil adhering to roots. Results indicated that nutrient concentrations on the basis of ash-free weight of root samples approached true nutrient concentrations of roots when the quality of soil adhering to roots was small, and the nutrient concentration of soil was much lower than the roots. Estimates of true nutrient concentrations of roots calculated from the information on the weight of soil adhering to roots and the nutrient concentration of the soil were satisfactory in the prediction of nutrient content of roots for a range of soil-contamination. The factor which accounted for contamination, and helped estimation of true concentrations from measured concentrations, depended on the magnitude of soil contamination and the relative concentrations of nutrients in roots and soil. Wet separation (washing) of roots from soil compared with dry separation resulted in 24% loss of K. With various methods of storage of washed root samples, the level of soil contamination was 5-20% of the root sample. Submergence of roots in water for 15 days after washing reduced the concentration of N, P and K in roots to 84, 50 and 54% of those roots which were dried immediately following washing. The rate of nutrient loss from roots was greater for K than for N and P when washed samples were stored submerged. On the basis of this study, it is recommended that roots, after separation from soil, should be dried as soon as possible with a minimum exposure of roots to wet conditions. Estimates of soil adhering to roots, and nutrient concentration of the adhering soil, are required to infer correct concentrations of nutrients in root samples.

Skeleton weight-free oxygen consumption related to adaptations to environment and habits of six crustacean species

1. 1. Oxygen consumption in six crustacean species from the continental shelf of the NW Gulf of Mexico was related to the ash free weight per dry weight (afdw) gram of the tissue excluding the exoskeleton, suggesting a close relationship to their life strategies. 2. 2. Dry weight exoskeleton proportion varied among species, with highest values recorded in callapid brachyuran crab species (46.8–52.5%) against the values recorded in portunid crab (45.8–48%) and the shrimp species (26.7–35.7%). 3. 3. Oxygen consumption was related to afdw in each species according to the expression y = ax b , with b values ranging from 0.68 to 2.92. 4. 4. Rates of oxygen consumption per afdw/dw were larger in shrimps than in portunids and callapids, and was related to the morphophysiology and lifestyle of six species described; the former as the morphological design of the exoskeleton versus the muscle content in the species and the latter as the activity rate in the environment. 5. 5. The oxygen extraction efficiency, calculated from oxygen consumption, was higher in the eurytopic species Penaeus aztecus and Callinecies similis than in species restricted to the marine environment, hence considered as a response to environmental fluctuations.

A method to determine the adenylate energy charge of the Mytilus edulis by reversed-phase high performance liquid chromatography

A method for the determination of the adenylate energy charge of the mussel Mytilus edulis by making use of high performance liquid chromatography (HPLC) is described. The collection of the mussels is discussed and attention is paid to the extraction procedure. The separation of the adenine-nucleotides is achieved with reversed-phase ion-pair chromatography. The purity of the peaks is confirmed by enzymatic cleavage of the nucleotides with alkaline phosphatase. A method is presented to determine the absolute concentrations of the adenine-nucleotides related to the ash-free weight of the mussel.

Root Decomposition and Nutrient Flux Following Whole-Tree Harvest of Northern Hardwood Forest

Abstract Decomposition of roots of four dominant species (Acer saccharum, Betula alleghaniensis, Fagus grandifolia, Picea rubens) in a northern hardwood ecosystem was measured following whole-tree harvest of watershed 5 at Hubbard Brook Experimental Forest, New Hampshire. To quantify the importance of element release from tree root systems after forest harvest, measurements of macronutrient (N, K, P, Ca, Mg) release from roots of seven diameter (mm) classes (&amp;lt; 0.6, 0.6-1.0, 1.0-2.5, 2.5-5.0, 5-10, 10-20, 20-100) were combined with information on root system nutrient content. Decay of fine roots (all species) was initially rapid but declined abruptly after the first summer. Ash-free weight loss from small woody roots decreased with increasing root diameter and was much slower than decay rates for corresponding aboveground tissues (twigs and branches). Weight loss rates among species generally were not significantly different; however, large woody roots (10-100 mm diameter) of sugar maple decayed much more rapidly than the other species. Rapid release of K and Mg was observed for all roots. Initially high rates of N and P release were observed for fine roots, whereas these nutrients were effectively retained in decaying woody roots. Retention of Ca was observed for all roots, and significant accumulation of Ca was observed in the larger size classes of woody roots. Particularly for N and K, release from decaying roots was an important nutrient flux pathway supplying stream outflow and vegetation regrowth in the first two years following forest harvest. For Sci. 34(3):744-768.

Herbicide effects on soil arthropod dynamics and wheat straw decomposition in a North Carolina no-tillage agroecosystem

Herbicide combinations of paraquat, glyphosate, alachlor, linuron, fluazifopbutyl, aciflurofen, and bentazon were investigated for their impact on soil arthropod population dynamics and surface wheat straw decomposition (weight loss) within a North Carolina coastal plain agroecosystem. Herbicides were applied twice (preemergence and mid-bloom) at recommended field rates to soybeans no-till planted into wheat residue. Separate measurements were made for surface crop residue and soil-dwelling (0–3 cm depth) arthropods. Decomposition of herbicide (glyphosate) and nonherbicide-treated wheat straw residue was compared using mesh bag techniques. Decay rate constants were estimated for glyphosate and nonherbicide-treated wheat straw residue by fitting a two-component model to the data. Comparison of soil microarthropod numbers from herbicide and nonherbicide treatments showed no consistent trend, suggesting that abiotic factors such as soil temperature and moisture were probably more significant than herbicide effects in regulating soil microarthropod number and activity. Herbicides had no effect on soil macroarthropod number or activity until late in the season when macroarthropods were most abundant under weedy, no-tillage conditions. Moist soil and litter, low soil temperature, floral diversity, and high weed-seed availability probably enhanced macroarthropod numbers in nonherbicide treatments. Decomposition (ash-free weight loss) of nonherbicided, surface crop residues was more rapid than herbicide (glyphosate) treated, indicating that herbicide effects occur at the decomposer as well as producer level of agroecosystems.

Geochemical factors complicating the use of aufwuchs to monitor bioaccumulation of arsenic, cadmium, chromium, copper and zinc

Material accumulating on submerged glass slides was sampled from five sites associated with coal ash settling basins and a control site. Correlation analyses demonstrated a strong, positive correlation between the five elements, arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn) and concentrations of associated iron or manganese. Negative, weak or nonsignificant correlations were noted between the concentrations of these five elements and microfloral cell densities or per cent ash free weight of the material. Scanning electron microscopy and X-ray analyses indicated that the majority of the material was abiotic and the elemental levels associated with the abiotic components were generally higher than those of the biotic components. Hydrous iron and manganese oxides likely play dominant roles in determining the trace element concentrations in these procedurally-defined aufwuchs. These findings indicate the potential for misinterpretation of biomonitoring data employing procedurally-defined aufwuchs.

Variation in Caloric Content of Populations ofChoaborus punctipennisin Two Lakes of Different Depths

ABSTRACT Changes in the caloric content of the phantom midge, Chaoborus punctipennis were compared in lakes of 8 m and 26 m depth. Organisms were collected monthly from March through November. Mean caloric content was 6355 and 4534 cal/g ash-free weight in the shallow and deep lake, respectively. Variation in migration distance of the organisms between the two lakes was suggested as influencing the pronounced variation in caloric content.

Organic matter and major elements of the forest floors and soils in subalpine balsam fir forests

Forest floors, fallen branches and fallen tree boles were sampled in 13 balsam fir (Abiesbalsamea (L.) Mill.) stands in the subalpine zone (1220–1450 m) of the White Mountains in New Hampshire, U.S.A. These 13 stands were distributed in three sites of contrasting exposure, slope, and rockiness. Soil pits were excavated in three of the stands representing each of the three sites. The ash-free dry weights and major elemental contents of the forest floor and dead wood were compared along chronosequences following natural disturbances, between sites, and with other forest types. No significant trends in these components were found along chronosequence comparisons. For sites that are dissimilar in terms of physical position on the landscape and in the appearance of the trees, compensating biotic and abiotic factors apparently underlie the convergence in forest floor and soil characteristics, thereby eliminating site differences as well. The forest floor is massive; ash-free dry weight averages 92 200 kg•ha−1. Total soil profile ash-free weight is 323 600 kg•ha−1. The forest floor and mineral soil horizons are unusually rich in nitrogen and phosphorus, with weighted average ash-free nitrogen and phosphorus concentrations of 2.42 and 0.23%, respectively, in the forest floor. Total nitrogen and phosphorus contents of the forest floor are 2300 and 217 kg•ha−1, respectively. The weight and nitrogen and phorphorus contents of the fir forest floor are greater than that found in other regional forests and coniferous forests in general.

Species composition, diversity, biomass, and chlorophyll of periphyton in greasy creek, red rock creek, and the Arkansas River, Oklahoma

Seventy-nine taxa of periphyton were collected on Plexiglas plates at seven stations in the three streams between March, 1975, and February, 1976. More taxa and lower densities were generally observed at the upstream stations in the creeks than at the downstream stations resulting in greater species diversity values at the upstream stations. Species diversity was generally lower in the river than in the creeks, reflecting the lower numbers of taxa and the presence of several abundant species. Species diversity did not reflect extremes in physiochemical conditions. Although several different species were abundant in the streams during the present study, the most commonly occurring dominants were Gomphonema olivaceum and species belonging to the genera Navicula and Nitzschia. No consistent trend was observed in ash-free weight; however, the concentration of chlorophyll a was generally greater at the downstream stations in the creeks than at the upstream stations.

Breakdown and Colonization of Nothofagus Leaves in a New Zealand Stream

Leaves of mountain beech, Nothofagus solandri var. cliffortioides (Hook f.) Poole immersed in a New Zealand stream in 1 mm mesh bags lost 49 % of their initial dry weight in 152 d. Ash-free weight declined from 95.5 % to 87.3 % of dry weight, percent carbon fluctuated within 4 % of its initial level and protein increased from I % to 6 % of leaf dry weight. An absolute increase in protein occurred in the first 3 wk. Aquatic hyphomycetes did not colonize leaves extensively. Diatoms were found in small numbers and bacteria were abundant on newly fallen and older leaves. Bags were colonized by 19 invertebrate species of which larval Chironomidae and nymphs of a stonefly Spaniocerca zelandica Tillyard were most abundant. A maximum density of 15 invertebrates per g dry weight of leaf was recorded after 152 days, however, total numbers per bag and species composition varied little with time. Insect feeding on bacterially conditioned leaves probably accounted for much of the leaf weight loss during the study.

The role of termites in an equatorial rain forest ecosystem of West Malaysia : I. Population density, biomass, carbon, nitrogen and calorific content and respiration rate.

1. Density of nests, population number, biomass, nitrogen and carbon content, calorific content and respiration rate of termites were studied at Pasoh Forest, West Malaysia mainly with four dominant species of epigeous nest builders, Macrotermes carbonarius, Dicuspiditermes nemorosus type-a, type-b and Homallotermes foraminifer, to reveal their role in the ecosystem. 2. The density of nests or mounds was 15-41/ha in M. carbonarius, 60-110/ha in the two types of D. nemorosus and 85-165/ha in H. foraminifer. 3. The population number per nest or mound was about 88,000 in M. carbonarius, 45,000 in D. nemorosus type-a, 47,000 in D. nemorosus type-b and 13,000 in H. foraminifer. The population number per hectare was about 1.8x106 for M. carbonarius, 4.3x106 for D. nemorosus type-a, 5.2x106 for D. nemorosus type-b and 2.1x106 for H. foraminifer. 4. The ratio in number of workers to soldiers was 6.4 for M. carbonarius, 19.0 for D. nemorosus type-a, 23.1 for D. nemorosus type-b and 8.9 for H. foraminifer. The ratio in number of adults (workers plus soldiers) to larvae was 1.4 for M. carbonarius, 0.59 for D. nemorosus type-a, 1.76 for D. nemorosus type-b and 3.84 for H. foraminifer. 5. The number of adults per nest of D. nemorosus type-a, type-b and H. foraminifer was linearly correlated with the weight of nest on the log-log coordinates. 6. The ratio of dry body weight to live weight was 0.24-0.30 for workers, 0.19-0.29 for soldiers and 0.15-0.22 for larvae. 7. The ash content of termite body was 26-66% for workers, 2-24% for soldiers and 1-4% for larvae. 8. The carbon content ranged from 45% to 66% of ash-free dry weight and the nitrogen content from 5.6% to 12.6%. 9. The mean calorific value of termite body was 5.3 gcal/mg in workers and soldiers on an ash-free weight basis, but was greater in nymphs and winged reproductives in the nest (6.7-6.9 gcal/mg) owing probably to their large fat storage. 10. The relation of CO2 evolution rate to temperature in these termites was similar to what has been found in other insects. 11. The total biomass of the four termite species was estimated at 6.01 kg ash-free dry weight/ha, equivalent to 0.55 kg nitrogen/ha and 3.09 kg carbon/ha. 12. The role of the fungi cultivated by M. carbonarius on their fungus combs was discussed in relation to the nutrition of termites and the decomposition of leaf-litter with special reference to their nitrogen metabolism. The high nitrogen content of fungus spherules growing on fungus combs seemed to have an important bearing on the nutrition of termites. 13. It was concluded that the termites played a very important role in the organic matter decomposition cycle of Pasoh Forest.

Assimilation Efficiency of Gammarus pseudolimnaeus (Amphipoda) Feeding on Fungal Mycelium or Autumn-Shed Leaves

Dry weight, ash-free weight, protein and energy content of food and faeces of Gammarus pseudolimnaeus Bousfield on different diets were compared. When feeding on elm or maple leaves, approximatately 10 % of the dry weight, 14-18 % of the protein, and 17-19 % of the energy of the ingested material was assimilated. When mycelium of various fungi which commonly decompose leaves in streams was offered, Gammarus assimilated 42.6-75.6 % of the dry weight, 73.3-96.4 % of the protein, and 67.9-83.2 % of the energy of the food ingested. These results and the presumable preference of detritius-feeders for leaf areas with higheshyphal concentrations indicate that the significance of fungal substances in the diet of leaf-eating animals may be considerably higher than suggested by estimates of the average microbial biomass per unit weight of decomposing leaves.

Zooplankton of the St. Lawrence Great Lakes — Species Composition, Distribution, and Abundance

Recent studies of zooplankton of the St. Lawrence Great Lakes have concentrated on a broad synoptic coverage of sampling stations and repeated cruises throughout a growing season. This has resulted in a considerable amount of detail about seasonal changes in species composition, total numbers, and vertical and horizontal distributions. Investigators have treated the data to show differences in distribution over the lakes on a cruise and cruise mean averages for each lake, often weighted by area to provide relative abundance figures over the season and between lakes.Maximum numbers were observed in Lake Erie (225,000/m3). Considerably fewer organisms were found in periods of peak abundance in Lake Ontario (55,000/m3) and Lake Huron (22,000/m3). No firm estimates are available for Lake Superior but numbers from one cruise (8000/m3) indicate still lower values there. Biomass estimates (either as ash-free weight of material from planktonnet hauls or from conversions of numbers to biomass from dry weight factors for individual species) are highest for Lake Erie, but reflect the larger size of organisms in the other lakes, especially Huron and Superior.Species distributions are now reasonably well known for crustaceans, except in one or two taxa of the cladocerans Daphnia and Bosmina whose variability should be investigated more fully. Recent studies have been made on the rotifers, but their numbers, distribution, and ecological role is not fully defined. Similarly, the distribution and role of protozoan groups have been largely ignored.Several computer techniques are suggested for the handling and analysis of the large quantities of data generated on lakewide surveys including community coefficients and cluster analyses. More attention should be given to determining sampling intervals to obtain information which can precisely detect changes in abundance from year to year, and better population dynamics and production data are needed to relate zooplankton stocks to eutrophication.

Ingestion and Growth in Sericostoma personatum (Trichoptera) in Relation to the Nitrogen Content of Ingested Leaves

Sericostoma personatum Spence was given autumn-shed leaves with differing nitrogen content: Fagus silvatica L. 1.33 % N of ash free weight, Picea abies (L.) Karst. 1.48 % N, Quercus borealis Michx. 2.15 % N, and Alnus glutinosa (L.) Gaertn. 4.82 % N. Leaves were preferred in the sequence Alnus Quercus Fagus/Picea. Ingestion by Sericostoma was significantly lower when fed Alnus than Fagus, Picea, and Quercus. Growth was significantly greater on Alnus and Quercus than on Picea and Fagus. Gross growth efficiency (G/I), calculatedon the basis of ash free weight, was 1.53-9.38 % and was positively correlated with leaf nitrogen. Calculated on a nitrogen basis, G/I was 13-22 %. The nitrogen content of the detritus may explain the low utilization efficiencies commonly reported for detritivores.