Adaptive vegetation management is time-consuming and requires long-term colony monitoring to obtain reliable results. Although vegetation management has been widely adopted, the only method existing ...at present for evaluating the habitat conditions under management involves observations over a long period of time. The presence of reactive oxygen species (ROS) has long been used as an indicator of environmental stress in plants, and has recently been intensely studied. Among such ROS, hydrogen peroxide (H2O2) is relatively stable, and can be conveniently and accurately quantified. Thus, the quantification of plant H2O2 could be applied as a stress indicator for riparian and aquatic vegetation management approaches while evaluating the conditions of a plant species within a habitat. This study presents an approach for elucidating the applicability of H2O2 as a quantitative indicator of environmental stresses on plants, particularly for vegetation management. Submerged macrophytes and riparian species were studied under laboratory and field conditions (Lake Shinji, Saba River, Eno River, and Hii River in Japan) for H2O2 formation under various stress conditions. The results suggest that H2O2 can be conveniently applied as a stress indicator in environmental management.
Purpose
Hulunbuir steppe has flat terrain and wide riparian zone of rivers and lakes on it. Owing to climate change, these riparian zones are often submerged or dried. This not only results in the ...instability of biodiversity in these regions but also affects the soil biogeochemical cycles. Soil C:N:P ecological stoichiometry plays a vital role in predicting and understanding the balance of multiple chemicals in ecological interactions. However, few studies have examined the soil C:N:P ecological stoichiometry in riparian zones of Hulunbuir steppe under different submergence states. Our objectives were to explore whether submergence frequencies impact soil C:N:P stoichiometry and identify the key factors.
Materials and methods
Four study sites were selected along the Hui river in Hulunbuir steppe, and three plots of different submergence frequencies, high (HF-sub, 5 to 7 times per year), moderate (MF-sub, 2 to 3 times per year), and low (LF-sub, unflooded or flooded once per year), were selected for each study site. Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), their ecological stoichiometric ratios (soil C:N, N:P, and C:P), soil ammonia nitrogen (NH
4
+
-N), nitrate nitrogen (NO
3
−
-N), available phosphorus (AP), soil pH, electrical conductivity (EC), soil moisture content (SMC), soil bulk density (SBD), porosity, and hardness were measured and analyzed.
Results and discussion
The results indicated that soil C:N:P ecological stoichiometry was notably affected by submergence frequency across the four study sites (
P
< 0.05). SOC, TN, TP, and their stoichiometric ratios changed regularly with the submergence frequency change, whereas their trends were inconsistent at different drainage basins. Soil C:N decreased with the decrease in submergence frequency but kept in a narrow scope, whereas the N:P and C:P were changed greatly under different submergence frequencies. Further analysis found that these significant variations in N:P and C:P were mainly due to the changes in soil TP which suggested there might be a P limitation in the riparian zones. The results of redundancy analysis (RDA) and path analysis indicated that soil AP and NO
3
−
-N were the key indirect factors affecting soil C:N:P ecological stoichiometry under different submergence frequencies, and SMC was an indirect factor.
Conclusions
We demonstrated that the soil C:N:P ecological stoichiometry was significantly affected by the submergence frequency in the riparian zones of Hulunbuir steppe. Soil N:P and C:P were more susceptible to change than C:N under different submergence frequencies. If the contents of soil AP and NO
3
−
-N were appropriate, soil C:N:P ecological stoichiometry will be more beneficial to regulating the cycle and balance of soil nutrient elements in the riparian zones, which can promote the riparian zones to provide better ecological functions.
Distributed models and a good knowledge of the catchment studied are required to assess mitigation measures for nitrogen (N) pollution. A set of alternative scenarios (change of crop management ...practices and different strategies of landscape management, especially different sizes and distribution of set-aside areas) were simulated with a fully distributed model in a small agricultural catchment. The results show that current practices are close to complying with current regulations, which results in a limited effect of the implementation of best crop management practices. The location of set-aside zones is more important than their size in decreasing nitrate fluxes in stream water. The most efficient location is the lower parts of hillslopes, combining the dilution effect due to the decrease of N input per unit of land and the interception of nitrate transferred by sub-surface flows. The main process responsible for the interception effect is probably uptake by grassland and retention in soils since the denitrification load tends to decrease proportionally to N input and, for the scenarios considered, is lower in the interception scenarios than in the corresponding dilution zones.
The long-term capacity of riparian zones in regulating groundwater nitrate fluxes is not well understood. This study analyses patterns of nitrate removal for the period 1994–2012 at two sites in a ...river floodplain that have received high groundwater nitrate loading from a large upland aquifer for over 32 years. During the study, mean NO₃⁻–N concentrations entering the riparian zone varied between 20–30 and 30–42 mg/L at the upstream and downstream sites respectively, but did not show any clear inter-annual trend. A permeable sand layer in the riparian zone is underlain by a regional aquitard at a depth of 5–6 m and 4 m at the upstream site and downstream site respectively. Denitrification resulted in a decline in nitrate concentrations as lateral groundwater flow in the sand layer interacted with buried peat and channel bar deposits that range up to 3 m in depth at both riparian sites. This interaction was greater at the downstream site where the organic deposits extend down to <1 m from the aquitard in some locations. At the upstream site nitrate removal efficiency in the sand layer, at depths of 3–4 m ∼20 m from the river bank, declined from 68 % in 1996–1998 to 42 % in 2009–2012. A smaller decline from 92 to 82 % occurred in the sand layer 10 m from the river bank during the study. In contrast, no clear pattern of change was evident at the downstream site where a nitrate removal efficiency of 98–100 % occurred at the river bank in most years between 1994 and 2012. These data suggest that the long-term nitrate removal performance of some riparian zones may decline if carbon availability for denitrification becomes limited as a result of variations in the quantity, quality and location of subsurface organic deposits that interact with deeper groundwater flowpaths.
Riparian zones are an important strategy to mitigate N and P export to streams. However, their efficiency with respect to nitrate (NO₃ ⁻), ammonium (NH₄ ⁺), or soluble reactive phosphorus (SRP) in ...groundwater remains uncertain in the US Midwest. This study investigates water table fluctuations and NO₃ ⁻, NH₄ ⁺, and SRP concentration dynamics in two riparian zone types (outwash vs. glacial till) common in the upper US Midwest. During low water table periods, NO₃ ⁻ removal was 93 % at WR (outwash site), and 75 % at LWD (glacial till site); but during high water table periods, NO₃ ⁻ removal efficiencies dropped to 50 % at WR, and 14 % at LWD. Median seasonal mass fluxes of NO₃ ⁻ removed at WR (9.4–21.7 mg N day⁻¹ m⁻¹ of stream length) and LWD (0.4–1.9 mg N day⁻¹ m⁻¹) were small compared to other riparian zones in glaciated landscapes. The WR site was a small SRP sink (0.114 and 0.118 mg day⁻¹ m⁻¹ during the dry period and wet period, respectively), while LWD acted as a small SRP source to the stream (0.004 mg day⁻¹ m⁻¹ during the dry period; 0.075 mg day⁻¹ m⁻¹ during the wet period). Both LWD and WR acted as sources of NH₄ ⁺ to the stream with mass fluxes ranging from 0.17 to 7.75 mg N day⁻¹ m⁻¹. Although riparian zones in the US Midwest provide many ecosystem services, results suggest they are unlikely to efficiently mitigate N and P pollution in subsurface flow.
Stream functioning is affected by allochthonous and autochthonous energy sources, organic matter decomposition and the structure and composition of the aquatic community. The presence of non-native ...tree species in the riparian zone may affect stream functioning. Thus, we quantified the allochthonous organic matter input to streams from native tree species and
Hovenia dulcis
, a non-native species, over a year, and we evaluated litter colonization and decomposition by aquatic invertebrates. The input of native organic matter was greater in Winter and Spring. On the other hand, the input of
H. dulcis
was higher in Autumn. The annual contribution of native organic matter was twofold greater than that of
H. dulcis
and was correlated with rainfall.
H. dulcis
leaf litter had decomposition rates that were three- to fourfold greater than those of native leaf litter. The invertebrate abundance and richness, and functional feeding groups did not vary between native and non-native leaf litter. We conclude that the presence of
H. dulcis
in the riparian zone changed the input patterns of allochthonous organic matter into streams. Furthermore,
H. dulcis
litter broke down faster than that of native species and did not directly affect the associated invertebrate community. However, the dominance of this species in riparian zones causes homogenisation of environment, resulting in changes in the composition of other biological communities (e.g., fungi and fish).
Over the past century, the natural flow regimes of the major western U.S. rivers have been altered by dams, flow regulation and diversion of water for human use. As a result, the floodplains of many ...rivers have become drier and more saline than in the pre-dam era, and riparian water tables have declined. These conditions have favored the replacement of native mesic trees such as
Populus spp. (cottonwood) and
Salix spp. (willow) by saltcedar, (
Tamarix ramosissima), an introduced, stress-tolerant shrub from Eurasia. Saltcedar is now the dominant woody species on many perennial rivers systems in the arid southwestern U.S. and northwest Mexico A review of the research literature shows that saltcedar has greater salt tolerance, drought tolerance, resistance to water stress, and fire tolerance than mesic native trees. On the other hand, under a natural flow regime, native trees are competitive with saltcedar in germination and establishment during a flood year and they have equal or faster growth rates. On rivers that still experience a pulse flood regime or where floods have been reestablished, cottonwood and willow have shown the ability to establish despite the presence of saltcedar. Contrary to previous reviews, the current evidence does not support the conclusion that saltcedar has unusually high evapotranspiration rates or leaf area index that would allow it to dessicate water courses. According to most researchers, an effective management strategy for saltcedar must include the return of a more dynamic hydrological regime to regulated rivers, allowing saltcedar and native trees to coexist to maximize the habitat value of the riparian zone.
Consumption of emergent aquatic insects by terrestrial invertebrates is a poorly resolved, but potentially important, mechanism of contaminant flux across ecosystem borders leading to contaminant ...exposure in terrestrial invertivores. We characterized the spatial extent and magnitude of contaminant transfer from aquatic sediments to terrestrial invertebrate predators by examining riparian araneid spiders, terrestrial insects, and emergent aquatic insects for stable isotopes and polychlorinated biphenyls (PCBs, sum of 141 congeners) at Lake Hartwell, (Clemson, South Carolina, USA). PCB concentrations in aquatic insects were orders of magnitude higher than in terrestrial insects. Aquatic insect consumption by spiders (as indicated by δδ
13
C and δδ
15
N), PCB concentrations in spiders, and aquatic prey availability were greatest at the shoreline and declined inland, while terrestrial prey availability was invariant with distance. These patterns indicate PCB transfer to spiders through consumption of emergent aquatic insects extending to a distance of ∼∼5 m inland. Measurable, but much lower, PCBs were present in insect predators dominated by social wasps up to 30 m inland. These results illustrate the importance of emergent insects as vectors of contaminant transfer from lake sediments to riparian food webs, and that spiders are key predators in this process.
Little is known about the impact of agricultural legacy on subsurface biogeochemical processes in the years following restoration of riparian wetlands (WLs). More knowledge is also needed on the ...relative importance of seasons, precipitation events, and inputs of water and nutrients driving nitrogen (N), phosphorus (P), sulfur (S), and greenhouse gas (GHG) (N2O, CO2, CH4) dynamics in these systems. This investigation of a riparian zone comprising a restored WL area and a nonrestored well‐drained alluvium (AL) area in the United States Midwest revealed that despite successful hydrological restoration a decade earlier, biogeochemical conditions in the WL area remained less anoxic than in natural WLs, and not significantly different from those in the AL area. No significant differences in N, P, S, and C compound concentrations or fluxes were observed between the AL and WL areas. Over the duration of the study, nitrate (NO3−) and soluble reactive phosphorus appeared to be primarily driven by hillslope contributions. Ammonium (NH4+), sulfate (SO42−), and CO2 responded strongly to seasonal changes in biogeochemical conditions in the riparian zone, while N2O and CH4 fluxes were most influenced by large rewetting events. Overall, our results challenge overly simplistic assumptions derived from direct interpretation of redox thermodynamics, and show complex patterns of solutes and GHGs at the riparian zone scale.
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