Temperate forests cover 16% of the global forest area. Within these forests, the understorey is an important biodiversity reservoir that can influence ecosystem processes and functions in multiple ways. However, we still lack a thorough understanding of the relative importance of the understorey for temperate forest functioning. As a result, understoreys are often ignored during assessments of forest functioning and changes thereof under global change. We here compiled studies that quantify the relative importance of the understorey for temperate forest functioning, focussing on litter production, nutrient cycling, evapotranspiration, tree regeneration, pollination and pathogen dynamics. We describe the mechanisms driving understorey functioning and develop a conceptual framework synthesizing possible effects of multiple global change drivers on understorey‐mediated forest ecosystem functioning. Our review illustrates that the understorey's contribution to temperate forest functioning is significant but varies depending on the ecosystem function and the environmental context, and more importantly, the characteristics of the overstorey. To predict changes in understorey functioning and its relative importance for temperate forest functioning under global change, we argue that a simultaneous investigation of both overstorey and understorey functional responses to global change will be crucial. Our review shows that such studies are still very scarce, only available for a limited set of ecosystem functions and limited to quantification, providing little data to forecast functional responses to global change.

Coastal urbanized areas in Southern California experience frequent beach water quality warnings in summer due to high concentrations of fecal indicator bacteria (FIB). Remediation can be difficult, as sources are often unknown. During two summers, we sampled three urbanized watersheds in Santa Barbara, CA at sites with historically high FIB concentrations to determine if human fecal matter was influencing water quality. By quantification of a human-specific Bacteroides marker (HBM), human waste was evidenced throughout both transects, and concentrations were highest in the discharges of several flowing storm drains. The HBM concentrations in storm drain discharges varied by up to 5 orders of magnitude on the same day. While the exact points of entry into the storm drain systems were not definitively determined, further inspection of the drain infrastructure suggested exfiltrating sanitary sewers as possible sources. The HBM and FIB concentrations were not consistently correlated, although the exclusive occurrence of high HBM concentrations with high FIB concentrations warrants the use of FIB analyses for a first tier of sampling. The association of human fecal pollution with dry weather drainage could be a window into a larger problem for other urbanized coastal areas with Mediterranean-type climates.

Separating storm drains and sanitary sewers is expected to control sewage pollution, for example, from combined sewer overflows, and to reduce excessive stormwater flow to wastewater treatment plants. However, sewage contamination has been found in such separated storm drain systems in urban areas during dry-weather flow. To determine whether transmission of sewage is occurring from leaking sanitary sewers directly to leaking separated storm drains, field experiments were performed in three watersheds in Santa Barbara, CA. Areas with high and low risks for sewage exfiltration into storm drains were identified, and rhodamine WT (RWT) dye pulses were added to the sanitary sewers. RWT was monitored in nearby storm drain manholes using optical probes set up for unattended continuous monitoring. Above-background RWT peaks were detected in storm drains in high-risk areas, and multiple locations of sewage contamination were found. Sewage contamination during the field studies was confirmed using the human-specific Bacteroidales HF183 and Methanobrevibacter smithii nifH DNA markers. This study is the first to provide direct evidence that leaking sanitary sewers can directly contaminate nearby leaking storm drains with untreated sewage during dry weather and suggests that chronic sanitary sewer leakage contributes to downstream fecal contamination of coastal beaches.

A two-stage biotrickling filter was developed for removing dimethyl sulfide (DMS) and hydrogen sulfide (H2S). The first biotrickling filter (ABF) was inoculated with Acidithiobacillus thiooxidans and operated without pH control, while the second biotrickling filter (HBF) was inoculated with Hyphomicrobium VS and operated at neutral pH. High DMS elimination capacities were observed in the HBF (8.2 g DMS m(-3) h(-1) at 90% removal efficiency) after 2 days. Maximal observed elimination capacities were 83 g H2S m(-3) h(-1) (100% removal efficiency) and 58 g DMS m(-3) h(-1) (88% removal efficiency) for the ABF and the HBF, respectively. The influence of a decreasing empty bed residence time (120 down to 30 sec) and the robustness of the HBF towards changing operational parameters (low pH, starvation, and DMS and H2S peak loadings) were investigated. Suboptimal operational conditions rapidly resulted in lower DMS removal efficiencies, but recovery of the HBF was mostly obtained within a few days. The H2S removal efficiency in the ABF, however, was not influenced by varying operational conditions. In both reactors, microbial community dynamics of the biofilm and the suspended bacteria were investigated, using denaturing gradient gel electrophoresis (DGGE). After a period of gradual change, a stable microbial community was observed in the HBF after 60 days, although Hyphomicrobium VS was not the dominant microorganism. In contrast, the ABF biofilm community was stable from the first day and only a limited bacterial diversity was observed. The planktonic microbial community in the HBF was very different from that in the biofilm.