Jörg Lewandowski

Long term effects of phosphorus precipitations with alum in hypereutrophic Lake Süsser See (Germany)

Precipitation and inactivation of phosphorus (P) by the addition of aluminum (Al) is a widely applied lake restoration measure. Many studies about short-term effects are reported, but little is known about long-term effects. To reduce this lack of knowledge we investigated the German hardwater lake, Süsser See, which was treated almost annually from 1977 to 1992 with aluminum sulfate (alum). We conducted sediment core experiments in laboratory, as well as in situ investigations of sediment and pore water. The treatment is clearly recognizable in sediment depth profiles as increases of total phosphorus, NaOH-extractable phosphorus, and NaOH-extractable aluminum. The molar ratio of added Al to additionally bound P is approximately 2.1:1. Pore water profiles of soluble reactive phosphorus taken in situ and in sediment core experiments, as well as sorption batch experiments, illustrate that the Al(OH)3 layers sorptive capacity is still not exhausted with further P sorption occurring in different P fractions. The P release of the sediment is affected by the magnitude of the downward flux into the P sorbing layer. However, sediment core experiments and a modeling exercise indicate that a buried P sorbing layer has little or no effect on the P release of the uppermost fresh sediment layers.

Fate of organic micropollutants in the hyporheic zone of a eutrophic lowland stream: Results of a preliminary field study

Many rivers and streams worldwide are impacted by pharmaceuticals originating from sewage. The hyporheic zone underlying streams is often regarded as reactive bioreactor with the potential for eliminating such sewage-born micropollutants. The present study aims at checking the elimination potential and analyzing the coupling of hydrodynamics, biogeochemistry and micropollutant processing. To this end, two sites at the lowland stream Erpe, which receives a high sewage burden, were equipped and sampled with nested piezometers. From temperature depth profiles we determined that at one of the sites infiltration of surface water into the aquifer occurs while exfiltration dominates at the other site. Biogeochemical data reveal intense mineralization processes and strictly anoxic conditions in the streambed sediments at both sites. Concentrations of the pharmaceuticals indomethacin, diclofenac, ibuprofen, bezafibrate, ketoprofen, naproxen and clofibric acid were high in the surface water and also in the subsurface at the infiltrating site. The evaluation of the depth profiles indicates some attenuation but due to varying surface water composition the evaluation of subsurface processes is quite complex. Borate and non-geogenic gadolinium were measured as conservative wastewater indicators. To eliminate the influence of fluctuating sewage proportions in the surface water, micropollutant concentrations are related to these indicators. The indicators can cope with different dilutions of the sewage but not with temporally varying sewage composition.

Retention and early diagenetic transformation of phosphorus in Lake arendsee (Germany) : consequences for management strategies

Repeated sediment core investigations over one decade, mass balance calculations, and vertical flux measurements by traps and dialysis samplers, were used to determine P retention rates, release potential, and early diagenetic transformation processes in the sediment of Lake Arendsee (Germany). Sediment cores were dated by varve counting, by 137 cesium, and by a distinct layer originating from a restoration attempt in 1995, which involved the capping of the sediment with calcium rich material from the lake shore. P retention rates and the internal P cycle have not been altered by the sediment capping. The sharp decline of total P content within the first two centimeters of the sediment shows that diagenetic P mobilization is a rapid process. The temporary P pool in the sediment, calculated from core analysis (mean ± SE: 709 ± 82mg m -2 , n = 7), was small compared to the rates of hypolimnetic SRP increase (10.7 ± 0.45 mg m -2 d -1 , 1992-1997) and total P losses in the epilimnion caused by sedimentation (11.7 ± 0.53 mg m -2 d -1 , 1992-1997), both of the latter calculated by mass balances during summer stratification. Without additional supply of freshly settled material, the temporary P pool in the sediment would be exhausted in less than three months. The fast P release of freshly settled material was also demonstrated during summer by the three times higher vertical P sedimentation rates calculated on the basis of mass balance data, compared to rates determined on the basis of cylindrical traps, in which some P was released during four weeks exposure time. The driving process for the rapid P release in Lake Arendsee is the remineralisation of organic P. This study demonstrates that high hypolimnetic P accumulation rates are not always correlated with a large total or potentially mobile P pool in the sediment. In lakes with small temporary P pools in the sediment, a decrease of P in the water body would immediately decrease the hypolimnetic P accumulation in summer; capping or dredging as in-lake measures are ineffective in such lakes.

Tube‐dwelling invertebrates: tiny ecosystem engineers have large effects in lake ecosystems

There is ample evidence that tube-dwelling invertebrates such as chironomids significantly alter multiple important ecosystem functions, particularly in shallow lakes. Chironomids pump large water volumes, and associated suspended and dissolved substances, through the sediment and thereby compete with pelagic filter feeders for particulate organic matter. This can exert a high grazing pressure on phytoplankton, microorganisms, and perhaps small zooplankton and thus strengthen benthic-pelagic coupling. Furthermore, intermittent pumping by tube-dwelling invertebrates oxygenates sediments and creates a dynamic, three-dimensional mosaic of redox conditions. This shapes microbial community composition and spatial distribution, and alters microbe-mediated biogeochemical functions, which often depend on redox potential. As a result, extended hotspots of element cycling occur at the oxic-anoxic interfaces, controlling the fate of organic matter and nutrients as well as fluxes of nutrients between sediments and water. Surprisingly, the mechanisms and magnitude of interactions mediated by these organisms are still poorly understood. To provide a synthesis of the importance of tube-dwelling invertebrates, we review existing research and integrate previously disregarded functional traits into an ecosystem model. Based on existing research and our models, we conclude that tube-dwelling invertebrates play a central role in controlling water column nutrient pools, and hence water quality and trophic state. Furthermore, these tiny ecosystem engineers can influence the thresholds that determine shifts between alternate clear and turbid states of shallow lakes. The large effects stand in contrast to the conventional limnological paradigm emphasizing predominantly pelagic food webs. Given the vast number of shallow lakes worldwide, benthic invertebrates are likely to be relevant drivers of biogeochemical processes at regional and global scales, thereby mediating feedback mechanisms linked to climate change.

Understanding process dynamics at aquifer‐surface water interfaces: An introduction to the special section on new modeling approaches and novel experimental technologies

[1] This paper introduces the special section on “new modeling approaches and novel experimental technologies for improved understanding of process dynamics at aquifer-surface water interfaces.” It is contextualizing the framework for the 27 research papers of the special section by firth identifying research gaps and imminent challenges for ecohydrological research at aquifer-surface water interfaces and then discussing the specific paper contributions on (i) new developments in temperature/heat tracing at GW-SW interfaces, (ii) new methods to capture the temporal and spatial variability of groundwater—surface water exchange, (iii) new approaches in modeling aquifer-river exchange flow, and (iv) new concepts and advanced theory of groundwater—surface water exchange.

Decision support for the selection of an appropriate in-lake measure to influence the phosphorus retention in sediments

Many in-lake measures which aimed to influence the phosphorus retention in lake sediments have failed to improve the trophic state of the lakes. The present paper introduces a systematic approach to select an appropriate in-lake measure. Before selecting an in-lake measure the goal of the measure should be defined, the problems of the lake must be identified, and the probability of success must be estimated. The proposed decision support consists of two parts. Part A, pre-selection, excludes inappropriate measures. It uses six criteria, which are mainly based on a simple mass-balance model, and the targets of restoration. The criteria describe the magnitude of the external versus the internal phosphorus loading, the dynamics of the internal load, and the lake morphometry. Each measure is weighted differently with respect to importance and suitability by specific quantified limits. Part B, selection, uses qualitative criteria, which are specific to the measure in question. Checking these criteria will help to select a measure with a low risk of failure. The suggested decision support is illustrated in flow charts and exemplified by Lake Arendsee in Germany.

Ecohydrological interfaces as hot spots of ecosystem processes

The movement of water, matter, organisms, and energy can be altered substantially at ecohydrological interfaces, the dynamic transition zones that often develop within ecotones or boundaries between adjacent ecosystems. Interdisciplinary research over the last two decades has indicated that ecohydrological interfaces are often “hot spots” of ecological, biogeochemical, and hydrological processes and may provide refuge for biota during extreme events. Ecohydrological interfaces can have significant impact on global hydrological and biogeochemical cycles, biodiversity, pollutant removal, and ecosystem resilience to disturbance. The organizational principles (i.e., the drivers and controls) of spatially and temporally variable processes at ecohydrological interfaces are poorly understood and require the integrated analysis of hydrological, biogeochemical, and ecological processes. Our rudimentary understanding of the interactions between different drivers and controls critically limits our ability to predict complex system responses to change. In this paper, we explore similarities and contrasts in the functioning of diverse freshwater ecohydrological interfaces across spatial and temporal scales. We use this comparison to develop an integrated, interdisciplinary framework, including a roadmap for analyzing ecohydrological processes and their interactions in ecosystems. We argue that, in order to fully account for their nonlinear process dynamics, ecohydrological interfaces need to be conceptualized as unique, spatially and temporally dynamic entities, which represents a step change from their current representation as boundary conditions at investigated ecosystems.

Alteration of Chironomus plumosus ventilation activity and bioirrigation-mediated benthic fluxes by changes in temperature, oxygen concentration, and seasonal variations

Abstract.  Burrowing benthic organisms promote water and solute fluxes across the sediment–water interface. Water and solutes penetrate the burrow walls and are transported into/out of the sediment when organisms flush their burrows with overlying water. Few studies have been done to investigate bioirrigation under shifting environmental conditions. We experimentally quantified bioirrigation by Chironomus plumosus larvae in the laboratory at 3 ranges of O2 saturation (low, medium, and high O2 concentrations), 2 temperatures (10 and 20°C), and over different seasons. We measured ventilation activities with O2 and flow-velocity microsensors, flow velocities during pumping periods with color tracers, pumping rates with conductivity exchange experiments, and rates of advective and diffusive water influx into the sediment by influx assays (NaCl was the tracer in both latter experiments). O2 saturations <12% extended pumping durations/h, whereas saturations <3% decreased pumping durations to ∼0. Flow velocities were 2× higher when O2 saturation was >50% than when it was <10%. Rising temperatures altered larval pumping (higher pumping frequency, lower pumping length) and increased flow velocity. Hence, pumping rate and rates of water influx were significantly higher at 20 than at 10°C. Seasonal variations in bioirrigation occurred despite constant laboratory conditions, i.e., the rate of water influx was significantly higher in spring/summer than in autumn. Our study shows that temporally varying environmental conditions should be considered when evaluating bioirrigation-mediated benthic fluxes across the sediment–water interface.

Bioirrigation by Chironomus plumosus: advective flow investigated by particle image velocimetry

Abstract Bioirrigation by tube-dwelling macrozoobenthos species causes an advective flow of overlying water through the burrow lumen. Particle image velocimetry (PIV) and color tracer measurements were used to measure flow velocities. The volumetric flow rate was calculated based on measured velocities and visual observation of larval body movements. Investigations were done with Chironomus plumosus (Diptera:Chironomidae) larvae and pupae. During pumping periods, flow velocity was 15.0 ± 10.7 (with color tracers: 13.6 ± 1.7) mm/s and volumetric flow rate was 40 ± 24 (with color tracers: 30.9 ± 3.9) µL/s for larvae. For pupae, these values were only 5.1 ± 0.7 mm/s and 11 ± 1 µL/s, respectively. Pupae conduct no filter feeding, so our results indicate that high volumetric flow rates occur because of filter-feeding. Furthermore, PIV measurements revealed the filtering effect of C. plumosus bioirrigation activity. A projection of the measured volumetric flow rate to Lake Müggelsee in Berlin, Germany (745 4th-instar larvae/m2), resulted in a flow of 1.3 m3 m−2 d−1. A volume equivalent to the water body of the lake is being pumped through the sediment every 4.8 d. This emphasizes the importance of burrow ventilation and filter-feeding for ecosystems.

Effects of bioirrigation of non-biting midges (Diptera: Chironomidae) on lake sediment respiration

Bioirrigation or the transport of fluids into the sediment matrix due to the activities of organisms such as bloodworms (larvae of Diptera, Chironomidae), has substantial impacts on sediment respiration in lakes. However, previous quantifications of bioirrigation impacts of Chironomidae have been limited by technical challenges such as the difficulty to separate faunal and bacterial respiration. This paper describes a novel method based on the bioreactive tracer resazurin for measuring respiration in-situ in non-sealed systems with constant oxygen supply. Applying this new method in microcosm experiments revealed that bioirrigation enhanced sediment respiration by up to 2.5 times. The new method is yielding lower oxygen consumption than previously reported, as it is only sensitive to aerobic heterotrophous respiration and not to other processes causing oxygen decrease. Hence it decouples the quantification of respiration of animals and inorganic oxygen consumption from microbe respiration in sediment.