Retention of contaminants and its controlling factors in constructed and semi-natural floodplain soils in urban river systems

The retention of floods is one of the most relevant ecosystem function of urban floodplains, which is often improved by the construction of retention ponds and other water management measures. Retention ponds are connected to the river in a direct or a parallel arrangement and can be constructed as dry or wet retention pond under normal run-off conditions. Carbon sequestration, nutrient and contaminant regulation and recreation are further important ecosystem functions provided by the floodplain soils. However, with ongoing urbanization these ecosystem functions are significantly endangered. In our study we analyze the soil-based ecosystem functions of two river catchments in the City of Hamburg. The presentation will focus on the retention of contaminants in sediments and soils of eleven retention ponds and ten flooded areas within one catchment. The amount and concentrations of contaminants will be analyzed and compared between the retention ponds and flooded areas. Furthermore, controlling factors on the contaminant amount and concentration like grain size distribution, land-use within the headwaters and others will be investigated. Finally, we will give an assessment on the current contaminant retention in this specific urban catchment area

Bewertung der Verfügbarkeit von nicht extrahierbaren PAK-Rückständen im Boden

Polyzyklische aromatische Kohlenwasserstoffe (PAK) bilden im Boden nicht extrahierbare Rückstände (NER) aus. Ziel dieser Untersuchungen war es, die Verfügbarkeit von 14 C-markierten NER nach Anwendung unterschiedlicher Stressbedingungen zu charakterisieren und somit zu einer Bewertung der Stabilität von NER unter sich verändernden Umweltbedingungen beizutragen. Sowohl biologische als auch physikalische Behandlungen führten zu keiner relevanten Freisetzung von 14 C-Aktivität aus NER. Lediglich die chemische Destabilisierung von organischen Metallkomplexen mit EDTA zeigte einen Effekt auf die Stabilität der NER. Eine Freisetzung von 14 C-Aktivität in extrahierbarer Form fand statt. Entweder handelt es sich dabei um zuvor physikalisch eingeschlossene Moleküle oder um lösliche organische Substanz (DOM)

Conversions of woodland to smallholder agriculture decreases soil organic carbon and nutrient stocks in semi-arid southern Africa

Southern African drylands are characterized by rapid deforestation, among others, related to the ongoing conversion of woodland to smallholder agriculture through slash-and-burn practices. However, empirical data on the impacts of this land-use conversion on soil fertility is rare. Our study in NE Namibia and SW Zambia aimed at quantifying the changes in soil organic carbon (SOC) and nutrient stocks upon the conversion from woodland to smallholder agriculture. We selected a total of 11 sampling clusters with a 1-km radius from two landscapes that differed in soil characteristics. Each cluster contained one or two 30 m x 30 m plots in agricultural fields and one plot in woodland, which was the reference land use. Plots within a cluster were carefully selected to have similar topographic- and soil characteristics. The selected agricultural fields ranged in age from 2 to 26 years, here age was based on the first year of agricultural usage. Moreover, we only selected agricultural fields that were established immediately after clearing of the woodland. In each plot, we measured SOC and N, and other nutrient (P, K, Ca, Mg and Na) contents and stocks down to 1-m and 0.4-m depth, respectively. In both landscapes, we found that conversions from woodland to smallholder agriculture in NE Namibia and SW Zambia decreased the topsoil (0-10-cm depth) contents and stocks of SOC and the soil nutrients N, Ca and Mg. The SOC and soil nutrient losses increased with increasing age of the agricultural fields. Soil K and Na contents did not significantly differ between woodland and agriculture. The effect of this land-use conversion on P content was not consistent between the studied landscapes

Responses of sap velocity in Acacia mellifera trees to soil water availability, vapour pressure deficit and global radiation

Acacia mellifera (multi-stem deciduous tree) is one of the dominant woody species responsible for bush encroachment in southern African savannahs. However, very little is known on water use, transpiration or xylem sap flow of A. mellifera. We analyzed the responses of sap velocity in A. mellifera to soil moisture, vapour pressure deficit and global radiation. This knowledge is necessary to improve hydrological modelling and will as such contribute to our understanding of the impacts of bush encroachment in (semi) arid savannahs on the soil water balance. We monitored sap velocities at two sites that differed in tree density in a semi-arid thornbush savannah in central Namibia (mean annual precipitation = 346 mm). Sap velocities were derived using the Heat Ratio Method. Measurements were done in four periods of 3-4 months between November 2014 and September 2016. The measurement periods covered the transitions between the dry and rainy season and vice versa, and the dry season. In two of these periods we did measurements at all stems of three trees per site (a total of 17-19 stems), while in the other two periods sap velocities were measured on one stem per tree for six to eight trees per site. Preliminary results indicate that the day-to-day fluctuations in cumulative daily sap velocity showed a three-phase interaction with soil water tension (minimum soil water tension of four sensors to 1-m depth). Phase I: At soil water tension < ~ pF 2.5, soil water tension had little influence on sap velocities, and fluctuations in sapflow seemed to be related to VPD and global radiation. Phase II: At soil water tensions between ~ pF 2.5 and ~ pF 3.2, sap velocities were negatively related to soil water tension. Phase III: At soil water tensions > ~ pF 3.2 no sap flow could be detected. The study was done in the framework of SASSCAL (Southern African Science Service Centre for Climate Change and Adaptive Land Management) granted by the German Federal Ministry of Education and Research (BMBF)

A space-time hybrid hourly rainfall model for derived flood frequency analysis

For derived flood frequency analysis based on hydrological modelling long continuous precipitation time series with high temporal resolution are needed. Often, the observation network with recording rainfall gauges is poor, especially regarding the limited length of the available rainfall time series. Stochastic precipitation synthesis is a good alternative either to extend or to regionalise rainfall series to provide adequate input for long-term rainfall-runoff modelling with subsequent estimation of design floods. Here, a new two step procedure for stochastic synthesis of continuous hourly space-time rainfall is proposed and tested for the extension of short observed precipitation time series. First, a single-site alternating renewal model is presented to simulate independent hourly precipitation time series for several locations. The alternating renewal model describes wet spell durations, dry spell durations and wet spell intensities using univariate frequency distributions separately for two seasons. The dependence between wet spell intensity and duration is accounted for by 2-copulas. For disaggregation of the wet spells into hourly intensities a predefined profile is used. In the second step a multi-site resampling procedure is applied on the synthetic point rainfall event series to reproduce the spatial dependence structure of rainfall. Resampling is carried out successively on all synthetic event series using simulated annealing with an objective function considering three bivariate spatial rainfall characteristics. In a case study synthetic precipitation is generated for some locations with short observation records in two mesoscale catchments of the Bode river basin located in northern Germany. The synthetic rainfall data are then applied for derived flood frequency analysis using the hydrological model HEC-HMS. The results show good performance in reproducing average and extreme rainfall characteristics as well as in reproducing observed flood frequencies. The presented model has the potential to be used for ungauged locations through regionalisation of the model parameters.BMBF/FKZ:033068

The Emergence of Clostridium difficile Infection among Peripartum Women: A Case-Control Study of a C. difficile Outbreak on an Obstetrical Service

Objective. An outbreak of 20 peripartum Clostridium difficile infections (CDI) occurred on the obstetrical service at the University of Washington Medical Center (UWMC) between April 2006 and June 2007. In this report, we characterize the clinical manifestations, describe interventions that appeared to reduce CDI, and determine potential risk factors for peripartum CDI. Methods. An investigation was initiated after the first three peripartum CDI cases. Based on the findings, enhanced infection control measures and a modified antibiotic regimen were implemented. We conducted a case-control study of peripartum cases and unmatched controls. Results. During the outbreak, there was an overall incidence of 7.5 CDI cases per 1000 deliveries. Peripartum CDI infection compared to controls was significantly associated with cesarean delivery (70% versus 34%; P = 0.03 ), antibiotic use (95% versus 56%; P = 0.001), chorioamnionitis (35% versus 5%; P = 0.001), and the use of the combination of ampicillin, gentamicin, and clindamycin (50% versus 3%; P < 0.001 ). Use of combination antibiotics remained a significant independent risk factor for CDI in the multivariate analysis. Conclusions. The outbreak was reduced after the implementation of multiple infection control measures and modification of antibiotic use. However, sporadic CDI continued for 8 months after these measures slowed the outbreak. Peripartum women appear to be another population susceptible to CDI

Randomized Trial of Antibiotics in Addition to Tocolytic Therapy to Treat Preterm Labor

Objective: The objective of this study was to assess whether antibiotic therapy plus tocolysis given to women in preterm labor would prolong pregnancy compared with tocolysis alone