Characterising the hydrological regime of an ungauged temporary river system: a case study

Temporary streams are characterised by specific hydrological regimes, which influence ecosystem processes, groundwater and surface water interactions, sediment regime, nutrient delivery, water quality and ecological status. This paper presents a methodology to characterise and classify the regime of a temporary river in Southern Italy based on hydrological indicators (HIs) computed with long-term daily flow records. By using a principal component analysis (PCA), a set of non-redundant indices were identified describing the main characteristics of the hydrological regime in the study area. The indicators identified were the annual maximum 30- and 90-day mean (DH4 and DH5), the number of zero flow days (DL6), flow permanence (MF) and the 6-month seasonal predictability of dry periods (SD6). A methodology was also tested to estimate selected HIs in ungauged river reaches. Watershed characteristics such as catchment area, gauging station elevation, mean watershed slope, mean annual rainfall, land use, soil hydraulic conductivity and available water content were derived for each site. Selected indicators were then linked to the catchment characteristics using a regression analysis. Finally, MF and SD6 were used to classify the river reaches on the basis of their degree of intermittency. The methodology presented in this paper constitutes a useful tool for ecologists and water resource managers in the Water Framework Directive implementation process, which requires a characterisation of the hydrological regime and a ‘river type’ classification for all water bodies.     

Storm flow export of metolachlor from a coastal plain watershed

Abstract

During an 18‐month (1994–1995) survey of the surface water in an Atlantic Coastal Plain watershed, metolachlor was most frequently detected during storm flow events. Therefore, a sampling procedure, focused on storm flow, was implemented in June of 1996. During 1996, three tropical cyclones made landfall within 150 km of the watershed. These storms, as well as several summer thunderstorms, produced six distinct storm flow events within the watershed. Metolachlor was detected leaving the watershed during each event. In early September, Hurricane Fran produced the largest storm flow event and accounted for the majority of the metolachlor exports. During the storm event triggered by Hurricane Fran, the highest daily average flow (7.5 m² s^‐1) and highest concentration (5.1 μg L^‐1) ever measured at the watershed outlet were recorded. Storm flow exports leaving the watershed represented 0.1 g ha^‐1 or about 0.04% of active ingredient applied.     

Hydraulic performance of a proposed in situ photocatalytic reactor for degradation of MTBE in water

Methyl tert-butyl ether (MTBE) groundwater remediation projects often require a combination of technologies resulting in increasing the project costs. A cost-effective in situ photocatalytic reactor design, Honeycomb II, is proposed and tested for its efficiency in MTBE degradation at various flows. This study is an intermediate phase of the research in developing an in situ photocatalytic reactor for groundwater remediation. It examines the effect of the operating variables: air and water flow and double passages through Honeycomb II, on the MTBE removal. MTBE vaporisation is affected by not only temperature, Henry’s law constant and air flow to volume ratio but also reactor geometry. The column reactor achieved more than 84% MTBE removal after 8 h at flows equivalent to horizontal groundwater velocities slower than 21.2 cm d⁻¹. Despite the contrasting properties between a photocatalytic indicator methylene blue and MTBE, the reactor efficiency in degrading both compounds showed similar responses towards flow (equivalent groundwater velocity and hydraulic residence time (HRT)). The critical HRT for both compounds was approximately 1 d, which corresponded to a velocity of 21.2 cm d⁻¹. A double pass through both new and used catalysts achieved more than 95% MTBE removal after two passes in 48 h. It also verified that the removal efficiency can be estimated via the sequential order of the removal efficiency of one pass obtained in the laboratory. This study reinforces the potential of this reactor design for in situ groundwater remediation.     

Forest owners’ perceptions of ecotourism: Integrating community values and forest conservation

The use of forest land for ecotourism has been well accepted due to its ability to provide income to local people and to conserve the forest. Preparing the forest with infrastructure to attract and educate visitors has been reported of importance. This study applied Q methodology in a small rural community of the State of Puebla, Mexico, to reveal forest owners’ perceptions to build infrastructure in their forest as part of their ecotourism project. It also discloses forest owners’ underlying motives to use their forest for ecotourism. Ecotourism is perceived as a complementary activity to farming that would allow women to be involved in community development. Low impact infrastructure is desired due to forest owners’ perception to preserve the forest for the overall community well-being.     

Seasonal water quality vs. flow relationships in a small regulated stream

The relationship of a water quality constituent with respect to flow measured at a stream monitoring station can give valuable information about the watershed and in-stream processes about the constituent in question. Seasonal dependency patterns often reveal relationships which would be unnoticed if all data are treated together. The aim of this study is to examine water quality constituent concentration vs. flow in a regulated small stream in order to detect seasonal relationships and to interpret them with regard to watershed processes. Expected relationship patterns have been observed for some water quality constituent like conductivity, suspended solids, etc. Some unexpected relationships have been detected which arise from the particular hydrologic regime of the stream and the surrounding watershed. The information gained can be used in watershed management studies to control contaminants reaching waterways.     

Darcian preferential water flow and solute transport through bimodal porous systems: Experiments and modelling

Soils often exhibit a variety of small-scale heterogeneities such as inter-aggregate pores and voids which partition flow into separate regions. In this paper a methodological approach is discussed for characterizing the hydrological behaviour of a heterogeneous clayey–sandy soil in the presence of structural inter-aggregate pores. For the clay soil examined, it was demonstrated that, coupling the transfer function approach for analyzing BTCs and water retention data obtained with different methods from laboratory studies captures the bimodal geometry of the porous system along with the related existence of fast and slow flow paths. To be effectively and reliably applied this approach requires that the predominant effects of the soil hydrological behaviour near saturation be supported by accurate experimental data of both breakthrough curves (BTCs) and hydraulic functions for high water content values. This would allow the separation of flow phases and hence accurate identification of the processes and related parameters.     

Macroinvertebrate community in relation to water quality and riparian land use in a substropical mountain stream,China

Exploring how water quality and land use shape the benthic macroinvertebrate community composition is of widespread interest in biodiversity conservation and environmental management. In this study, we investigated the structures of benthic macroinvertebrate assemblages and their environmental controls in terms of water quality and riparian land use in the Jinshui River, China. We carried out three campaigns including wet season (August 2009), dry season (November 2009), and normal season (April 2010) based on the hydrological regime in Jinshui basin. The result showed that macroinvertebrate assemblage variations were better explained by water quality factors than land use based on variance partitioning procedure. The land use of 2 km upstream from the sampling sites had explained more variation than that of the whole riparian zone in upstream catchment on macroinvertebrate community, and land use of 2 km upstream also had more interactions with water quality. Canonical correspondence analysis (CCA) indicated that the elements or nutrient of magnesium (Mn), selenium (Se), strontium (Sr), silicon (Si), dissolved inorganic nitrogen (DN), sulfur (S), total organic carbon (TOC), and total nitrogen (TN) in water exhibited a strong relationship with macroinvertebrate assemblages. However, the variance in water quality explained by land use was lower than that explained by water quality in rivers using redundancy analysis. Our study suggested that proximate factors (i.e., water quality) were more important to interpret the macroinvertebrate community compared to ultimate factors (i.e., land use) for macroinvertebrate assemblages in river system.     

Discrete and time-integrated sampling for chromium load calculations in a watershed with an impoundment reservoir at an exceptionally low water level

Instantaneous (discrete) and time-integrated (composed) samples were collected during a 19-week period in a watershed impacted by discontinuous discharges from local tanneries (Carpathians Mountains, Poland). Existence of the impoundment reservoir in this watershed allowed investigation of its role in chromium transport. In collected samples, dissolved and particulate chromium concentrations were measured to apportion both loads. This study has demonstrated that the impoundment reservoir retains not only particulate but also a dissolved form of chromium and its efficiency reaches 74–94 %. Sampling results proved that chromium contamination in the investigated river is variable and discontinuous. Discrete sampling can lead to an underestimation of chromium contamination level (up to 78 %), especially when illegal/unexpected discharges occur in the watershed. A discrete sampling regime also produces less reliable data for contaminant budget calculations, especially in sites where strong variability of contamination is anticipated, while at the output from reservoirs, the load can be reasonably estimated using this mode of sampling.     

Impact of river flow modification on wetland hydrological and morphological characters

A good number of researchers investigated the impact of flow modification on hydrological, ecological, and geomorphological conditions in a river. A few works also focused on hydrological modification on wetland with some parameters but as far the knowledge is concerned, linking river flow modification to wetland hydrological and morphological transformation following an integrated modeling approach is often lacking. The current study aimed to explore the degree of hydrological alteration in the river and its effect on downstream riparian wetlands by adopting advanced modeling approaches. After damming, maximally 67 to 95% hydrological alteration was recorded for maximum, minimum, and average discharges. Wavelet transformation analysis figured out a strong power spectrum after 2012 (damming year). Due to attenuation of flow, the active inundation area was reduced by 66.2%. After damming, 524.03 km² (48.9% of total pre-dam wetland) was completely obliterated. Hydrological strength (HS) modeling also reported areas under high HS declined by 14% after post-dam condition. Wetland hydrological security state (WSS) and HS matrix, a new approach, are used to explore wetland characteristics of inundation connectivity and hydrological security state. WSS was defined based on lateral hydrological connectivity. HS under critical and stress WWS zones deteriorated in the post-dam period. The morphological transformation was also well recognized showing an increase in area under the patch, edge, and a decrease in the area under the large core area. All these findings established a clear linkage between river flow modification and wetland transformation, and they provided a good clue for managing wetlands.

     

Improved land cover and emission factors for modeling biogenic volatile organic compounds emissions from Hong Kong

This paper describes a study of local biogenic volatile organic compounds (BVOC) emissions from the Hong Kong Special Administrative Region (HKSAR). An improved land cover and emission factor database was developed to estimate Hong Kong emissions using MEGAN, a BVOC emission model developed by Guenther et al. (2006). Field surveys of plant species composition and laboratory measurements of emission factors were combined with other data to improve existing land cover and emission factor data. The BVOC emissions from Hong Kong were calculated for 12 consecutive years from 1995 to 2006. For the year 2006, the total annual BVOC emissions were determined to be 12,400 metric tons or 9.82 × 10⁹ g C (BVOC carbon). Isoprene emission accounts for 72%, monoterpene emissions account for 8%, and other VOCs emissions account for the remaining 20%. As expected, seasonal variation results in a higher emission in the summer and a lower emission in the winter, with emission predominantly in day time. A high emission of isoprene occurs for regions, such as Lowest Forest-NT North, dominated by broadleaf trees. The spatial variation of total BVOC is similar to the isoprene spatial variation due to its high contribution. The year to year variability in emissions due to weather was small over the twelve-year period (?1.4%, 2006 to 1995 trendline), but an increasing trend in the annual variation due to an increase in forest land cover can be observed (+7%, 2006 to 1995 trendline). The results of this study demonstrate the importance of accurate land cover inputs for biogenic emission models and indicate that land cover change should be considered for these models.     

Material flow analysis of pollutants in Taiwan

We present a material flow analysis (MFA) of biological oxygen demand (BOD5) and suspended solids (SS) in estuaries located on the northern and southern coasts of Taiwan. Using data from 1992–2000, we examine human economic activities in each watershed to predict associated pollutant flows. This estimate is compared to data collected at monitoring stations. The ratio allows us to calculate each river system's ability to assimilate and decompose these pollutants, its self-purification capacity. Our results show that over six times as much BOD5 reaches the northern estuary from the urban watershed that in the south. More SS reaches the southern estuary than the north due to more intense land disturbance. Trends for pollutant flows to the northern estuary threaten its capacity to meet sustainability criteria. Trends in the south show a receding threat. We suggest management objectives to enhance prospects for sustaining environmental quality in these two critical regions.     

Linking national agrarian policy to deforestation in the Peruvian Amazon: a case study of Tambopata, 1986-1997

Amazonian deforestation rates vary regionally, and ebb and flow according to macroeconomic policy and local social factors. We used remote sensing and field interviews to investigate deforestation patterns and drivers at a Peruvian frontier during 1986-1991, when rural credit and guaranteed markets were available; and 1991-1997, when structural adjustment measures were imposed. The highest rate of clearing (1.5% gross) was observed along roads during 1986-1991. Roadside deforestation slowed in 1991-1997 (0.7% gross) and extensive regrowth yielded a net increase in forest cover (0.5%). Deforestation along rivers was relatively constant. Riverside farms today retain more land in both crops and forest than do roadside farms where pasture and successional growth predominate. Long-term residents maintain more forest on their farms than do recent colonists, but proximity to urban markets is the strongest predictor of forest cover. Future credit programs must reflect spatial patterns of development and ecological vulnerability, and support the recuperation of fallow lands and secondary forest.     

Using satellite imagery to locate innovative forest management practices in Nepal

There is a critical need to locate innovative forest management institutions that significantly impact forest cover change. This research presents an initial "proof of concept" methodology which combines deforestation theory with satellite image change analysis to identify forested areas that, theoretically, should probably not be there. Ten such "forest anomalies" are identified using temporal analysis of Landsat TM imagery of the Chitwan district in Nepal, linked with a GIS database on roads and a visual estimation of topography. A rapid field reconnaissance is undertaken to determine which of these anomalies exhibit interesting forest management innovations. Based on this information, one case is selected for detailed field study: this turns out to be a major case of community forestry and a premier ecotourism initiative that we were not aware of until we undertook this analysis. The utility and limitations of the method are described for monitoring trends in forest cover change.     

Phosphorus flows and use efficiencies in production and consumption of wheat, rice, and maize in China

Increasing fertilizer phosphorus (P) application in agriculture has greatly contributed to the increase of crop yields during the last decades in China but it has also increased P flows in food production and consumption. The relationship between P use efficiency and P flow is not well quantified at national level. In present paper we report on P flows and P use efficiencies in rice, wheat, and maize production in China using the NUFER model. Conservation strategies for P utilization and the impact of these strategies on P use efficiency have been evaluated. Total amounts of P input to wheat, rice, and maize fields were 1095, 1240, and 1128 Gg, respectively, in China, approximately 80% of which was in chemical fertilizers. The accumulation of P annually in the fields of wheat, rice, and maize was 29.4, 13.6, and 21.3 kg ha⁻¹, respectively. Phosphorus recovered in the food products of wheat, rice, and maize accounted for only 12.5%, 13.5%, and 3.8% of the total P input, or 3.2%, 2.6%, and 0.9% of the applied fertilizer P, respectively. The present study shows that optimizing phosphorus flows and decreasing phosphorus losses in crop production and utilization through improved nutrient management must be considered as an important issue in the development of agriculture in China.     

The effect of hydrological regime on the metal bioavailability for the wetland plant species Salix cinerea

The hydrological conditions on a site constitute one of the many factors that may affect the availability of potentially toxic trace metals for uptake by plants. Bioavailability of Cd, Mn and Zn in a contaminated dredged sediment-derived soil under different hydrological regimes was determined by measuring metal uptake by the wetland plant species Salix cinerea, both in field circumstances and in a greenhouse experiment. Longer submersion periods in the field caused lower Cd concentrations in leaves and bark. The wetland hydrological regime in the greenhouse experiment resulted in normal Cd and Zn concentrations in the leaves, while the upland hydrological regime resulted in elevated Cd and Zn concentrations in the leaves. Field observations and the greenhouse experiment suggest that a hydrological regime that creates or sustains a wetland is a potential management option that reduces metal bioavailability to willows. This would constitute a safe management option of metal-polluted, willow-dominated wetlands provided that wetland conditions can be maintained throughout the full growing season.     

Relevance of the Paraná River hydrology on the fluvial water quality of the Delta Biosphere Reserve

The increasing frequency of extreme events in large rivers may affect not only their flow, but also their water quality. In the present study, spatial and temporal changes in fluvial physico-chemical variables were analyzed in a mega-river delta during two extreme hydrological years (La Niña-El Niño) and related to potential explanatory factors. Basic water variables were evaluated in situ at 13 points (distant 2–35 km from each other) in watercourses of the Delta Biosphere Reserve (890 km²) in the Lower Paraná River (Argentina) in nine surveys (October 2008–July 2010) without meteorological tides. Samples for laboratory analyses were collected from each main river. Multivariate tests by permutations were applied. The period studied was influenced by a drought, within a long period dominated by low flows combined with dry weather and wildfires, and a large (10 years of recurrence) and prolonged (7 months) flood. The hydrological phase, followed by the season and the hydrological year (according to the ENSO event) were the principal explanatory factors of the main water quality changes, whereas the drainage sub-basin and the fluvial environment (river or stream) were secondary explanatory factors. During the drought period, conductivity, turbidity, and associated variables (e.g., major ions, silicon, and iron concentrations) were maximal, whereas real color was minimal. In the overbanking flood phase, pH and dissolved oxygen concentration were minimal, whereas real color was maximal. Dissolved oxygen saturation was also low in the receding flood phase and total major ion load doubled after the arrival of the overbanking stage. The water quality of these watercourses may be affected by the combination of several influences, such as the Paraná River flow, the pulses with sediments and solutes from the Bermejo River, the export of the Delta floodplain properties mainly by the flood, the season, and the saline tributaries to the Lower Paraná River. The high influence of the hydrology of this large river on the Delta fluvial water quality emphasizes the relevance of changes in its flow regime in recent decades, such as the seasonality attenuation. Considering that the effects of extreme events differ among and within fluvial systems, specific ecohydrological evaluations and powerful appropriate statistics are key tools to gain knowledge on these systems and to provide bases for suitable management measures in a scenario of climate change and increasing human alterations and demands.     

Influence of soil hydrological pathways on stream aluminium chemistry at Llyn Brianne, mid-wales

Storm runoff in afforested catchments at Llyn Brianne is acidic and Al-bearing. At baseflows, stream water is well-buffered with low Al levels. This paper presents the results of a study into how hydrological pathways account for these variations in stream-water chemistry. The investigation was carried out in the LI1 catchment; a 0.4-ha subcatchment covered by stagnohumic gley soils was monitored between October 1988 and September 1989. An instrumented hill-slope was established to identify the hydrological pathways that control the hydrochemistry of storm runoff draining from the subcatchment. Perched watertables developed in the surface horizons of the soil during storm episodes and produced lateral flow above the impeding subsoil. This near-surface flow path was responsible for generating acid, Al-rich storm runoff. Some water drained vertically through the soil profile into the underlying slope drift; seepage from groundwater in the drift sustained baseflows. Buffering reactions in the groundwater zone reduced the acidity and Al levels of baseflows. These hydrochemical characteristics are likely to be representative of other areas of stagnohumic gley soils, which cover 19% of the LI1 catchment: these soils may therefore provide a substantial source of acid, Al-bearing storm runoff in LI1 and similar afforested catchments.     

Use of Revised Universal Soil Loss Equation (RUSLE) and Historical Imagery for Claims of Sedimentation of Lakes and Streams

The consequences of erosion and subsequent sedimentation of lakes and streams are many and widespread. The natural process of erosion can be accelerated by land cover changes with an increase in areas of impervious surfaces. Sediment is continually being transported along all streams in nature and can come from anywhere in the watershed. Lakes slow the rate of velocity of the water and allow the entrained sediment to settle and accumulate. When sediment impacts water impoundments, legal actions may result. Even with evidence of specific sediment release, the forensic analysis may not be an open-and-shut case. The author presents a method to investigate the validity of a legal claim of a sediment-impacted lake at the outfall of a mixed rural/urban watershed. By combining land use change, soils, elevation and precipitation data, a maximum possible annual sediment loss was approximately 154 tonne per hectare (15.4 kg/m²). Lacking evidence of specific historic events of erosion and subsequent sedimentation, this method provides an equitable means of determining compensatory damages. Using aerial and satellite imagery provided historical evidence of land cover change and examples of significant erosion in the watershed and not named in the lawsuit. The focus of the litigation started with the property adjoining the effected lake. The analysis provides a method to investigate erosion and subsequent sedimentation claims at a watershed-scale.     

Establishment of reference conditions for nutrients in an intensive agricultural watershed,Eastern China

Nutrient enrichment from nonpoint source pollution is one of the main causes of poor water quality and biotic impairment in many streams and rivers worldwide. The establishment of reference nutrient conditions in a river system is an essential but difficult task for water quality control. In the present study, the reference concentrations of total nitrogen (TN) and total phosphorus (TP) were estimated in an intensive agricultural watershed, the Cao-E River system of Eastern China. Based on a 3-year water quality monitoring data in the river system, three approaches were adopted to establish the reference concentrations of TN and TP, those are the 75th percentile of frequency distribution of nutrient concentrations in reference streams, the 25th percentile of frequency distribution of nutrient concentration in general streams (including reference and non-reference streams) and regression modeling. Results showed that the nutrient reference concentrations were slightly different from different approaches. By the three approaches, the average reference concentrations for TN and TP in the study system were 1.73?±?0.13 mg l^?1 and 55.23?±?4.77 μg l^?1 with CV of 7.39 % and 8.63 %, respectively. Accordingly, the reference concentrations for TN and TP were recommended to be 1.70 mg l^?1 and 55 μg l^?1, respectively. In the mountainous and intensive agricultural watershed, the major anthropogenic impacts to river water quality were the urban area percentage cover, cropland area with slopes 0–8°, and livestock and poultry waste loads density. These variables could account for 89.7 % and 80.3 % of the total variations for TN and TP concentration, respectively.     

Changes in Tree Growth,Biomass and Vegetation Over a 13-Year Period in the Swedish Sub-Arctic

This study was conducted in the Swedish sub-Arctic, near Abisko, in order to assess the direction and scale of possible vegetation changes in the alpine–birch forest ecotone. We have re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters. The plots were originally surveyed in 1997 and re-surveyed in 2010. Our study is unique for the area as we have quantitatively estimated a 19% increase in tree biomass mainly within the existing birch forest. We also found significant increases in the cover of two vegetation types—“birch forest-heath with mosses” and “meadow with low herbs”, while the cover of snowbed vegetation decreased significantly. The vegetation changes might be caused by climate, herbivory and past human impact but irrespective of the causes, the observed transition of the vegetation will have substantial effects on the mountain ecosystems.