Adjacent Aquatic Ecosystems Research Articles

Non-native earthworms in riparian soils increase nitrogen flux into adjacent aquatic ecosystems

Riparian zones are an important transition between terrestrial and aquatic ecosystems, and they function in nutrient cycling and removal. Non-native earthworms invading earthworm-free areas of North America can affect nutrient cycling in upland soils and have the potential to affect it in riparian soils. We examined how the presence of earthworms can affect riparian nutrient cycling and nutrient delivery to streams. Two mesocosm experiments were conducted to determine how (1) the biomass of earthworms and (2) earthworm species can affect nutrient flux from riparian zones to nearby streams and how this flux can affect streamwater nutrients and periphyton growth. In separate experiments, riparian soil cores were amended with one of four mixed earthworm biomasses (0, 4, 10, or 23 g m(-2) ash-free dry mass) or with one of three earthworm species (Aporrectodea caliginosa, Lumbricus terrestris, L. rubellus) or no earthworm species. Riparian soil cores were coupled to artificial streams, and over a 36-day period, we measured nutrient leaching rates, in-stream nutrient concentrations, and periphyton growth. Ammonium leaching increased with increasing biomass and was greatest from the A. caliginosa treatments. Nitrate leaching increased through time and increased at a greater rate with higher biomass and from cores containing A. caliginosa. We suggest that the overall response of increased nitrate leaching [90% of total nitrogen (N)] was due to a combination of ammonium excretion and burrowing by earthworms, which increased nitrification rates. During both experiments, periphyton biomass increased through time but did not differ across treatments despite high in-stream inorganic N. Through time, in-stream phosphorus (P) concentration declined to <5 microg l(-1), and periphyton growth was likely P-limited. We conclude that activities of non-native earthworms (particularly A. caliginosa) can alter biogeochemical cycling in riparian zones, potentially reducing the N-buffering capacity of riparian zones and altering stoichiometric relationships in adjacent aquatic ecosystems.

XANES Spectroscopic Analysis of Phosphorus Speciation in Alum‐Amended Poultry Litter

Aluminum sulfate (alum; Al(2)(SO(4))(3).14H(2)O) is used as a chemical treatment of poultry litter to reduce the solubility and release of phosphate, thereby minimizing the impacts on adjacent aquatic ecosystems when poultry litter is land applied as a crop fertilizer. The objective of this study was to determine, through the use of X-ray absorption near edge structure (XANES) spectroscopy and sequential extraction, how alum amendments alter P distribution and solid-state speciation within the poultry litter system. Our results indicate that traditional sequential fractionation procedures may not account for variability in P speciation in heterogeneous animal manures. Analysis shows that NaOH-extracted P in alum amended litters is predominantly organic ( approximately 80%), whereas in the control samples, >60% of NaOH-extracted P was inorganic P. Linear least squares fitting (LLSF) analysis of spectra collected of sequentially extracted litters showed that the P is present in inorganic (P sorbed on Al oxides, calcium phosphates) and organic forms (phytic acid, polyphosphates, and monoesters) in alum- and non-alum-amended poultry litter. When determining land application rates of poultry litter, all of these compounds must be considered, especially organic P. Results of the sequential extractions in conjunction with LLSF suggest that no P species is completely removed by a single extractant. Rather, there is a continuum of removal as extractant strength increases. Overall, alum-amended litters exhibited higher proportions of Al-bound P species and phytic acid, whereas untreated samples contained Ca-P minerals and organic P compounds. This study provides in situ information about P speciation in the poultry litter solid and about P availability in alum- and non-alum-treated poultry litter that will dictate P losses to ground and surface water systems.

Soil phosphorus cycling in an Antarctic polar desert

Soil phosphorus distribution and cycling in the McMurdo Dry Valleys is poorly understood despite its importance for contemporary Antarctic ecosystem processes. We present data from sequential chemical extractions of phosphorus pools from dry valley soils and sediments on tills across a gradient of surface exposure ages, and across potential weathering gradients in stream channels. The geologically old, but poorly weathered, soils of the dry valleys have large phosphorus pools relative to in situ biological requirements. These pools are dominated by unweathered P fractions, comprising between 60 and 90% of total soil phosphorus among sites occurring on tills ranging in surface exposure ages of approximately 10 3–10 6 yrs. Variation in total phosphorus concentration and availability are related to differences in the initial P content of these tills; Ross Sea tills contain basalts and kenyte which contribute to higher concentrations of phosphorus relative to soils developing on tills deposited by advances of the Taylor Glacier. At local scales, physicochemical gradients contribute to variation in weathering rates, altering the distribution of phosphorus among chemical fractions, which differ in their potential mobility and availability to microorganisms. For example, hyporheic stream sediments exhibit evidence of phosphorus weathering from primary minerals and loss relative to upland soils adjacent to stream channels. Dry valley landscapes (glaciers, lakes streams, soils) are hydrologically connected, providing a mechanism for phosphorus weathering and mobilization in soils and sediments to contribute to the nutrient budgets of adjacent aquatic ecosystems. We suggest that landscape history (till composition) and contemporary subsurface and stream hydrology are the primary controls over phosphorus cycling in the McMurdo Dry Valleys.

Evaluation of Limnological Responses to Recent Environmental Change and Caribou Activity in the Rivière George Region, Northern Québec, Canada

The influence of natural terrestrial disturbances on the limnology of northern lakes is little known, yet important for understanding the ecology of these remote ecosystems. The Rivière George Caribou Herd (RGCH) in northern Québec has undergone a large population increase since the 1950s, which has been accompanied by pronounced impacts (i.e., degradation of vegetation cover, soil erosion) on terrestrial environments of the Rivière George region. The goal of our study was to evaluate if the increased caribou activity and resulting terrestrial impacts have been accompanied by impacts on adjacent aquatic ecosystems. We studied the recent diatom assemblages (i.e., about the last two centuries) preserved in six sediment cores taken from lakes located in the most heavily impacted region, and in one core from a lake showing little evidence of recent caribou activity in the catchment basin. Core chronologies based on 210Pb dating techniques indicated that average mass sedimentation rates in this subarctic region were very low (0.0039 to 0.012 g cm–2 yr–1). Perhaps surprisingly, diatom assemblages from all seven cores showed very little change, indicating remarkably stable limnological conditions throughout the past ~200 yr. The lack of a signal from caribou activity is most likely due to (1) short-term impacts being too transitory to be registered in the sediment record, and (2) long-term impacts not representing a significant perturbation outside the natural variability of these aquatic ecosystems. In contrast to other arctic regions, the limnological stability of our study sites suggests that recent climatic change impacts have been negligible in this region of northern Québec, which seems to confirm climate model predictions that northern Québec and Labrador will remain climatically stable under global warming scenarios.

Evaluation of Limnological Responses to Recent Environmental Change and Caribou Activity in the Riviere George Region, Northern Quebec, Canada

The influence of natural terrestrial disturbances on the limnology of northern lakes is little known, yet important for understanding the ecology of these remote ecosystems. The Rivière George Caribou Herd (RGCH) in northern Québec has undergone a large population increase since the 1950s, which has been accompanied by pronounced impacts (i.e., degradation of vegetation cover, soil erosion) on terrestrial environments of the Rivière George region. The goal of our study was to evaluate if the increased caribou activity and resulting terrestrial impacts have been accompanied by impacts on adjacent aquatic ecosystems. We studied the recent diatom assemblages (i.e., about the last two centuries) preserved in six sediment cores taken from lakes located in the most heavily impacted region, and in one core from a lake showing little evidence of recent caribou activity in the catchment basin. Core chronologies based on 210Pb dating techniques indicated that average mass sedimentation rates in this subarctic region were very low (0.0039 to 0.012 g cm–2 yr–1). Perhaps surprisingly, diatom assemblages from all seven cores showed very little change, indicating remarkably stable limnological conditions throughout the past ~200 yr. The lack of a signal from caribou activity is most likely due to (1) short-term impacts being too transitory to be registered in the sediment record, and (2) long-term impacts not representing a significant perturbation outside the natural variability of these aquatic ecosystems. In contrast to other arctic regions, the limnological stability of our study sites suggests that recent climatic change impacts have been negligible in this region of northern Québec, which seems to confirm climate model predictions that northern Québec and Labrador will remain climatically stable under global warming scenarios.

Application of the forest–soil–water model (PnET-BGC/CHESS) to the Lysina catchment, Czech Republic

In this study a fully linked plant-soil-water model PnET-BGC/CHESS (Santore, R.C., 1996. PnET-BGC/CHESS model. Version P3NC115; Santore, R.C., 1999. Modeling forest soil response to chemical treatment at three sites in the Adirondack Mountains, New York) was evaluated and applied. Forest growth, hydrologic, and biogeochemical processes with emphasis on element cycling in forest and adjacent aquatic ecosystems were simulated for the Lysina catchment, Czech Republic. The PnET-BGC submodel expands calculations of forest productivity and water use of the earliest version of the PnET model to include decomposition processes and cycling of major nutrients and other elements. The CHESS submodel simulates abiotic soil chemical processes. The study catchment consists of Norway spruce ( Picea abies) plantations on Spodosols located in a granitic highland of western Bohemia. Forest growth, hydrology and biogeochemistry of the catchment were simulated for the period 1550–2050. Simulated concentrations of SO 4 2−, F −, Ca 2+, Mg 2+, Na +, K +, Fe T, Si, and monomeric Al were similar to streamwater concentrations measured in 1990–1994. The model moderately overpredicted H +, Cl − and DOC, and highly overpredicted NO 3 − and especially NH 4 +. A scenario of reductions of S inputs by 67% of 1991–1994 values in 1995–2050 showed a decrease in base saturation of soil of 2.5% between 1995 and 2050. Inputs of S reduced by 90% of current values showed an increase in soil base saturation after 2030. Scenarios of improved deposition of S showed desorption of previously stored S to drainage water which delayed recovery from inputs of acidic deposition.

Energy transformation by the supralittoral isopod Ligia dilatata Brandt

Energy flow was studied through a population of the supralittoral isopod Ligia dilatata Brandt, which inhabits kelp debris cast up on rocky shores. Mean annual standing crop ( B ̄ ) and production ( P) were estimated from field data to be 422 and 1582 kJ · m −1 of shoreline, respectively, giving a P B ̄ ratio of 3.7. Population consumption (C), egestion ( F), and respiration ( R) rates (123258, 88395, and 5194 kJ · m −1 · yr −1, respectively) were estimated from laboratory experiments. Energy lost through urinary excretion and DOM was considered to be negligible and was not estimated. Various efficiency ratios are used to characterize energy flow through the population: absorption efficiency ( (C−F) C ) is 28.3%, assimilation efficiency ( (P + R) C ) is 5.5% and gross growth efficiency ( P C ) a very low 1.3%. The ecological implications of the fast consumption and egestion rates coupled with low assimilation and growth efficiences are discussed, showing that L. dilatata must be regarded as energy transformers returning large amounts of suspended detritus to adjacent aquatic ecosystems.