Microeukaryotic plankton community dynamics under ecological water replenishment:Insights from eDNA metabarcoding

Ecological water replenishment(EWR)is an important strategy for river restoration globally,but timely evaluation of its ecological effects at a large spatiotemporal scale to further adjust the EWR schemes is of great challenge.Here,we examine the impact of EWR on microeukaryotic plankton communities in three distinct river ecosystems through environmental DNA(eDNA)metabarcoding.The three ecosystems include a long-term cut-off river,a short-term connected river after EWR,and long-term connected rivers.We analyzed community stability by investigating species composition,stochastic and deterministic dynamics interplay,and ecological network robustness.We found that EWR markedly reduced the diversity and complexity of microeukaryotic plankton,altered their community dynamics,and lessened the variation within the community.Moreover,EWR disrupted the deterministic patterns of community organization,favoring dispersal constraints,and aligning with trends observed in naturally connected rivers.The shift from an isolated to a temporarily connected river appeared to transition community structuring mechanisms from deterministic to stochastic dominance,whereas,in permanently connected rivers,both forces concurrently influenced community assembly.The ecological network in temporarily connected rivers post-EWR demonstrated significantly greater stability and intricacy compared to other river systems.This shift markedly bolstered the resilience of the ecological network.The eDNA metabarcoding insights offer a novel understanding of ecosystem resilience under EWR interventions,which could be critical in assessing the effects of river restoration projects throughout their life cycle.

Maintaining eco-health of urban waterscapes with imbedded integrating ecological entity： Experimental approach

An imbedded integrating ecological entity(IIEE) was designed to combine landscaping, replenishing-water purifying and ecosystem maintaining simultaneously. With this IIEE, within 15 d experiment, simulated replenish water(SRW) with high(SRW-Ⅰ) or low(SRW-Ⅱ) nutrients concentration was well purified. Relative removal rates of CODCr, TP, TN, Chl-a and turbidity reached 84.87%, 84.05%, 94.76%, 188.17%, 110.93% when dealing SRW-Ⅰ, and 52.62%, 90.05%, 82.44%, 166.15%, 202.99%, respectively, when dealing SRW-Ⅱ. The well grew flora and fauna of IIEE benefit eco-maintaining and landscaping. Separately, the maximal root and stem length-increments of Cyperus alternifolius Linn. were 26.1 mm and 28.4 mm, while for Potamogeton crispus Linn. 18.3 mm and 25.7 mm. Mortality for both Bellamya aeruginosa and Misgurnus anguillicaudatus was both under 2.96%. The analysis of variance(ANOVA) indicated that most experimental indexes in each group performed more significantly better than those in their control. All results indicated that the IIEE is a promising technology for future urban waterscapes construction.

Response of Soil Moisture to Rainfall Event in Black Locust Plantations at Different Stages of Restoration in Hilly-gully Area of the Loess Plateau, China

Precipitation plays an important role in the water supplies that support ecological restoration by sustaining large-scale artificial plantations in arid and semiarid regions, especially black locust(Robinia pseudoacacia) plantations(RP plantations), which are widely planted due to R. pseudoacacia being an excellent pioneer species. Characterizing the response of soil moisture to rainfall events at different stages of restoration is important for assessing the sustainability of restoration in RP plantations. In this study, we quantified the response of soil moisture to rainfall events at different years of restoration(15, 20 and 30 yr) representing different restoration stages in RP plantations in a typical hilly-gully area, i.e., the Yangjuangou Catchment, of the Loess Plateau, China. Over the growing season(June to September) of 2017, smart probes were placed at nine depths(10, 20, 40, 60, 80, 100, 120, 150, and 180 cm below the soil surface) to obtain volumetric soil water information at 30-min intervals in the three RP plantations. The advance of the wetting front was depicted, and the total cumulative water infiltration was measured. Soil moisture was mainly replenished by eight heavy rainfall events(mean rainfall amount = 46.3 mm), accounting for 88.7% of the rainfall during the growing season. The mean soil moisture content profiles of RP plantations at the three restoration stages were ordered as 30-yr(14.07%) > 20-yr(10.12%) > 15-yr(8.03%), and this relationship displayed temporal stability. Soil moisture was primarily replenished by rainfall at the 0-60 cm soil depth, and soil moisture remained stable below the 100-cm soil depth. The rainfall regime influenced the advancement of the wetting front. Here, a single rainfall event of 30 mm was the rainfall threshold for infiltration into the 60-cm soil layer. The total infiltration time ranged from 310.5-322.0 h, but no significant differences were found among RP plantations at different restoration stages. Young and old RP plantations had more total infiltration(more than 228.2 mm) and deeper infiltration depths(80-100 cm) than middle-aged plantations. The RP plantation at the intermediate restoration stage exhibited minimal total infiltration(174.2 mm) and a shallow infiltration depth(60 cm) due to the soil physical structure of the plot, which may have limited rain infiltration. More stand conditions that may affect infiltration should be considered for priority afforestation areas.