Plantation Catchment Research Articles

Cypermethrin insecticide residue, water quality and phytoplankton diversity in the lychee plantation catchment area

<abstract> <p>Lychee plantation areas are typically located at varying elevations on mountains to ensure proper drainage. This placement has direct effects on stream and river water flows and consequently influences pesticide residue, water quality and aquatic biodiversity. This research aims to examine the relationships between cypermethrin residue, water quality and phytoplankton diversity in the lychee plantation catchment area in Phayao Province, Thailand, from January to May 2022. The study area was divided into six sampling sites. Water samples were collected for the investigation of cypermethrin residual, physicochemical and biological water quality parameters. The water quality index was used as an overall measurement of water quality. The study also examined the diversity of phytoplankton species and the relationship among cypermethrin residue, water quality and phytoplankton diversity were studied using canonical correspondence analysis. The findings revealed an increasing trend of cypermethrin residue, with the maximum concentration reaching 29.43 mg/L in March. The trend of decreasing water quality scores from Station S1 to Station S5 indicated the influence of land use changes and human activities, especially in the community area (S5), which was characterized by deterioration of water quality. A total of 174 phytoplankton species were categorized into 5 divisions, with Chlorophyta accounting for 61.49% of the total, followed by Bacillariophyta (28.16%) and Cyanophyta (6.32%). The highest Shannon's diversity index and evenness were observed at Stations S3 and S4, respectively. The canonical correspondence analysis revealed an interesting relationship among cypermethrin residue, ammonia nitrogen, chlorophyll a and three algal species: <italic>Pediastrum simplex</italic> var. <italic>echinulatum</italic>, <italic>Pediastrum duplex</italic> var. <italic>duplex</italic> and <italic>Scenedesmus acutus</italic> at Station S3. This research implies that pesticide residue and water quality have a direct impact on phytoplankton distribution, illustrating the environmental challenges that occur in various geographical areas. This information can be applied to assist in the development of future sustainable land use management initiatives.</p> </abstract>

Linking evapotranspiration seasonal cycles to the water balance of headwater catchments with contrasting land uses

AbstractLand use affects evapotranspiration rates and is a primary driver of the catchment water balance. The water balance of two catchments in southeastern Australia dominated by either grazed pasture or blue gum (Eucalyptus globulus) plantation was studied, focusing on the patterns of evapotranspiration (ET) throughout the year. Rainfall, streamflow, and groundwater levels measured between 2015 and 2019 were combined to estimate annual ET using a water balance equation. In the pasture, eddy covariance was used to measure ET from the catchment. Sap flow measurements were used to estimate tree transpiration in May 2017–May 2018 and Feb 2019–Feb 2021 in two different plots within the plantation. The tree transpiration rates were added to interception, estimated as a percentage of annual rainfall, to calculate ET from the plantation catchment. ET in the pasture showed strong seasonal cycles with very low ET rates in summer and ET rates in spring that were larger than the transpiration rates in the plantation, where trees transpired consistently throughout the year. The estimated annual ET from the water balance equation was comparable to ET estimated from other measurements. In the pasture, ET on average accounted for 88% of annual rainfall, while ET in the plantation was on average 93% of rainfall, exceeding it in the years with annual rainfall lower than about 500 mm. The difference between the ET rates in the plantation and the pasture was approximately 30–50 mm y−1. The larger ET rates in the plantation were reflected in a gradual decrease in the groundwater storage. The larger ET rates were enough to cause a decrease in groundwater storage in the plantation but not in the pasture, where groundwater levels remained stable.

Sources and mean transit times of intermittent streamflow in semi-arid headwater catchments

Determining the sources and mean transit times (MTTs) of water that generates streamflows is important for understanding and managing headwater catchments. The sources and especially the MTTs of water that contributes to streamflow in seasonally intermittent streams are far less studied than for perennial streams. Here we use major ions, dissolved organic carbon, stable isotopes, radon and tritium to quantify the sources and MTTs of intermittent streamflows in three headwater catchments (Banool, McGill and Plantation) from a semi-arid area in southeast Australia. At the start of streamflows, the MTTs of stream water varied from 25 to 42 years in the 1.51 km2 Banool catchment, 3 to 4 years in the 3.38 km2 McGill catchment and 9 to 14 years in the 3.41 km2 Plantation catchment. Winter rainfall increased the relative contribution of younger waters in all three catchments. During higher winter streamflows, the MTTs of stream water reduced to ≤5 years in the Banool catchment and <1 year in the McGill and Plantation catchments. The sources of streamflow also differed between the catchments. Regional groundwater, which close to the stream has a residence time of several hundred years, dominated in the Banool catchment, whereas younger water (residence times of up to 9 years) stored in the riparian zone was the main source in the McGill and Plantation catchments. The differences in MTTs between the catchments may reflect land-use differences, especially the presence of plantation forests in the McGill and Plantation catchments. Overall, due to being less well-connected to the regional groundwater, the MTTs of these intermittent streams are far shorter than those reported for perennial headwater streams in southeast Australia. The short MTTs indicate that these intermittent streams are vulnerable to short-term variations in rainfall.

Flux and source of dissolved inorganic carbon in a headwater stream in a subtropical plantation catchment

Dissolved inorganic carbon (DIC) in headwater streams significantly contributes to the riverine CO2 emission to the atmosphere and oceans. However, understanding of the sources and mechanisms of DIC generation and mass balances of DIC flux in headwater streams at the scale of catchments remain poor and add to uncertainty in regional carbon estimates. In this study, the input and output of water fluxes and their chemical and isotopic compositions in a headwater stream were investigated from 2016 to 2019 in a subtropical plantation catchment. Our results showed that the headwater stream catchment experienced a net carbon loss of 262–4352 kg C km−2 yr−1 based on the water balance of annual precipitation, evapotranspiration, headwater stream and groundwater discharge, and change in soil water storage. The headwater stream exhibited comparable DIC flux (3561 ± 933 kg C km−2 yr−1) and higher DIC concentration (7.91 ± 3.13 mg L−1) than precipitation (3662 ± 682 kg C km−2 yr−1 and 2.63 ± 1.22 mg L−1, respectively). Differences in DIC concentration between precipitation and headwater stream were mainly controlled by soil CO2 dissolution, carbonate weathering, and their synergistic effects. Relative contributions to DIC fluxes in this headwater stream were 25.3 ± 5.2% by precipitation, 47.3 ± 6.2% by soil biological CO2, and 27.4 ± 7.3% by carbonate weathering. Our results indicated that the DIC-generating processes may result in an underestimation of soil biological CO2 efflux to the atmosphere. Further, soil carbonate weathering, and a net carbon loss at the scale of catchments may be overlooked in acid soils.

Particulate macronutrient exports from tropical African montane catchments point to the impoverishment of agricultural soils

Abstract. Agricultural catchments in the tropics often generate high concentrations of suspended sediments following the conversion of natural ecosystems. The eroded fine particles are generally enriched with carbon (TC) and nutrients (TN and TP) originating from the topsoil of agricultural land. Sediment-associated TC, TN and TP are an important loss to the terrestrial ecosystem and tightly connected to an increase in riverine particulate TC and nutrient export. Soil nutrient depletion can limit crop growth and yields, whereas an excess of nutrients in streams can cause eutrophication in freshwater systems. Streams in East Africa, with widespread land conversion from forests to agriculture, are expected to receive high loads of sediment-associated TC, TN and TP. In this study, we assess the effect of land use on particulate TC, TN and TP concentrations. Suspended sediments (time-integrated, manual-event-based and automatic-event-based sediment samples) were analysed for TC, TN and TP concentrations collected at the outlet of a natural montane forest (35.9), a tea-tree plantation (33.3) and a smallholder agriculture (27.2 km2) catchment in western Kenya during a wet sampling period in 2018 and a drier sampling period in 2019. Particulate TC, TN and TP concentrations were up to 3-fold higher (p&lt;0.05) in the natural forest catchment compared to fertilized agricultural catchments. However, because of higher sediment loads from the smallholder agriculture catchment, the total sediment-associated loads of TC, TN and TP were higher compared to the natural forest and tea-tree plantation catchment. The higher C:N ratios in the natural forest suggest that the particulate nutrients are of organic origin due to tighter nutrient cycles, whereas lower ratios in both agricultural catchments suggest a mixture of mineral and organic sediment sources. The findings of this study imply that with the loss of natural forest, the inherent soil fertility is progressively lost under the current low fertilization rates and soil management strategies.

Tropical Montane Forest Conversion Is a Critical Driver for Sediment Supply in East African Catchments

AbstractLand use change is known to affect suspended sediment fluxes in headwater catchments. There is however limited empirical evidence of the magnitude of these effects for montane catchments in East Africa. We collected a unique 4‐year high‐frequency data set and assessed seasonal sediment variation, water pathways, and sediment response to hydrology in three catchments under contrasting land use in the Mau Forest Complex, Kenya's largest tropical montane forest. Annual suspended sediment yield was significantly higher in a smallholder agriculture‐dominated catchment (131.5 ± 90.6 t km−2 yr−1) than in a tea‐tree plantation catchment (42.0 ± 21.0 t km−2 yr−1) and a natural forest catchment (21.5 ± 11.1 t km−2 yr−1) (p &lt; 0.05). Transfer function models showed that in the natural forest and the tea‐tree plantations subsurface flow pathways delivered water to the stream, while in the smallholder agriculture shallow subsurface and surface runoff were dominant. There was a delayed sediment response to rainfall for the smallholder agriculture and the tea‐tree plantations. A slow depletion in sediment supply suggests that the wider catchment area supplies sediment, especially in the catchment dominated by smallholder farming. In contrast, a fast sediment response and depletion in sediment supply in the natural forest suggests a dominance of temporarily stored and nearby sediment sources. This study shows that the vegetation cover of a forest ecosystem is very effective in conserving soil, whereas catchments with more bare soil and poor soil conservation practices generated six times more suspended sediment yield. Catchment connectivity through unpaved tracks is thought to be the main explanation for the difference in sediment yield.

Effects of local land-use on riparian vegetation, water quality, and the functional organization of macroinvertebrate assemblages

Land-use change is a principal factor affecting riparian vegetation and river biodiversity. In Chile, land-use change has drastically intensified over the last decade, with native forests converted to exotic forest plantations and agricultural land. However, the effects thereof on aquatic ecosystems are not well understood. Closing this knowledge gap first requires understanding how human perturbations affect riparian and stream biota. Identified biological indicators could then be applied to determine the health of fluvial ecosystems. Therefore, this study investigated the effects of land-use change on the health of riparian and aquatic ecosystems by assessing riparian vegetation, water quality, benthic macroinvertebrate assemblages, and functional feeding groups. Twenty-one sites in catchment areas with different land-uses (i.e. pristine forests, native forests, exotic forest plantations, and agricultural land) were selected and sampled during the 2010 to 2012 dry seasons. Riparian vegetation quality was highest in pristine forests. Per the modified Macroinvertebrate Family Biotic Index for Chilean species, the best conditions existed in native forests and the worst in agricultural catchments. Water quality and macroinvertebrate assemblages significantly varied across land-use areas, with forest plantations and agricultural land having high nutrient concentrations, conductivity, suspended solids, and apparent color. Macroinvertebrate assemblage diversity was lowest for agricultural and exotic forest plantation catchments, with notable non-insect representation. Collector-gatherers were the most abundant functional feeding group, suggesting importance independent of land-use. Land-use areas showed no significant differences in functional feeding groups. In conclusion, anthropogenic land-use changes were detectable through riparian quality, water quality, and macroinvertebrate assemblages, but not through functional feeding groups. These data, particularly the riparian vegetation and macroinvertebrate assemblage parameters, could be applied towards the conservation and management of riparian ecosystems through land-use change studies.

Runoff and soil erosion characteristics in different periods of an intensive forest management system in a tropical indonesian rainforest

Tropical Indonesian rainforest is managed using an Intensive Forest Management System (IFMS). The main activity is selective logging for timber harvesting and intensive line planting to enrich the standing stock. These activities signifi cantly alter the forest canopy cover and the hydrologic response of catchments, including peak discharge, direct runoff and soil erosion. Understanding the hydrologic effects in an IFMS is helpful to develop a forest management strategy. This study investigated the impact of vegetation changes on runoff and soil erosion characteristics in different periods of an IFMS resulting from their respective forestry treatments. This study was conducted in a natural tropical rainforest at Bukit Baka Experimental Catchment, Central Kalimantan, Indonesia. Runoff and soil erosion characteristics were investigated in three small catchments, a virgin forest catchment (C1), a 10-year-old line plantation catchment (C2) and a 1-year-old line plantation catchment (C3). The IFMS has increased in large scale of open forests and exposed the bare soil, especially in the early years after forest operation. This condition has changed drastically in the catchment hydrologic responses. The increase in discharge, direct runoff, and suspended sediment discharge in the C3 was higher than those in the C2 and C1, particularly for large rainfall events. The proportion of annual rainfall as water yield in the C1, C2, and C3 was 27, 30, and 41%, respectively. The annual suspended sediment yield in the C1, C2, and C3 was 0.15, 3.6, and 14.9 t ha −1 y −1 , respectively. The results showed that the magnitude of runoff and soil erosion depends on the interaction among the rainfall, forest cover changes, forest treatment applied and catchment characteristics. Ten years after forest operation, forest cover has recovery close to natural condition, but still there are differences in hydrological response. Controlling soil erosion during logging activities by reducing the impact of logging and combining ecologically based vegetation structure design is an effective way to control runoff and soil erosion.

A comparison of streamflow, salt and water balances in adjacent farmland and forest catchments in south‐western Victoria, Australia

AbstractA study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Influence of Plantation Establishment on Discharge Characteristics in a Small Catchment of Tropical Forest

A study was conducted on the impact of forest clearance on discharge from newly established Hopea odorata plantations catchment (14.4 ha). The stands were two years old when this study commenced in year 2006 and the data collection was carried out for two years. The forested catchment (C3) was clear-cut during the preparation of the forest plantation and catchment C1 was left undisturbed. Discharge and rainfall were measured continuously for two years. The discharge measured from years 1997 to 2003 was used also to determine the water yield before and after forest clear-cut. This study showed that the plantation catchment is more responsive to storm with higher total water yield than in the forested catchment. The effect of forest clear cutting to discharge was clearly shown by the increment in the amount following the clear-cut activities and time taken for the recovery of the discharge back to its original state was almost three years. The peak discharge in C3 also was affected in which the biggest change was obtained during the forest clear-cutting period compared with during calibration and after clearing periods. This study is useful as basis for improving the existing guidelines on forest plantation establishment.

Longer-term changes in streamflow following logging and mixed species eucalypt forest regeneration: The Karuah experiment

Summary The Karuah replicated paired catchment experiment was initiated in the 1970s to examine the hydrological effects of eucalypt-to-eucalypt forest succession in New South Wales, Australia. Treatments were conducted on 25.4–78.8% of the area of six small catchments in 1983. Five of the treated catchments experienced a significant increase in streamflow following forest disturbance, equivalent to annual water yield changes ranging from 120 mm to 319.6 mm which varied in proportion to the percentage of each catchment logged. This initial increase lasted for greater than 5 years in the logged and unburnt Bollygum (L−) catchment, but had returned to pre-treatment levels within 2.5 years in the logged and burnt (L+) Corkwood and Jackwood catchments, and within 2 years in the Kokata and Coachwood plantation catchments (P). A significant reduction in streamflow then occurred in three catchments – Corkwood (113.5 mm a−1), Bollygum (72.7 mm a−1) and Kokata (68.9 mm a−1) – but had returned to the pre-treatment level within 7 years post-harvest in the Corkwood catchment. A continuing suppression of streamflow after 27 years is evident in two of the catchments, Bollygum and Kokata, with Kokata experiencing a further decline from 2005 onwards to a mean annual reduction of 172.4 mm. By contrast a significant increase in streamflow relative to the pre-treatment level has been recorded in the Jackwood catchment after 23 years (157.6 mm a−1). Relative changes in streamflow measured in this experiment can be explained largely by changes in forest species composition, basal area and stocking rates. The eucalypt stands have variously self-thinned and in some cases forest growth appears to have been slowed by insect attack and bell miner associated dieback. Contrary to earlier published findings, while this study confirms that Mountain ash type water yield reductions can occur in other forest types, this response appears to be the exception rather than the rule. These findings have implications for the modelling and management of water yield impacts of mixed species eucalypt forest disturbance.

Impacts of wildfire and salvage harvesting on water quality and nutrient exports from radiata pine and eucalypt forest catchments in south-eastern Australia

Salvage harvesting may represent an important additional impact on sediment and nutrient transfer in forest environments affected by wildfire. However, few studies have examined the effect of this management practice on stream water quality and catchment nutrient exports. In this paper, we investigate nutrient losses following post-wildfire salvage harvesting of a radiata pine plantation catchment compared to an adjacent natural eucalypt forest catchment that was also burnt but not harvested. The study catchments form part of the long-term Cropper Creek Hydrology Project (established in 1975) that is situated in south-eastern Australia. Post-fire monitoring (2007–2009) involved collection of both weekly and flow proportional water samples that were compared with previously reported data from samples collected prior to the fire (1997–2003). It was found that median values of total suspended solids (TSS) and turbidity returned to pre-fire levels within 3 years in both catchments, whereas maximum levels during storm events in the harvested pine catchment continued to exceed the eucalypt catchment. This reflected a previously reported large increase in post-fire sediment exports from the harvested pine catchment that was a minimum 180 times the eucalypt catchment over the study period. In contrast, the impact of harvesting on solute concentrations (nitrate-N, P, S, Cl, Na, K, Ca, Mg) was minor and most solutes returned to pre-fire levels within 2–3 years in both catchments. Nutrient exports from the pine catchment exceeded the eucalypt catchment by 102 times for particulate P associated with suspended material compared to 1.9–4 times for solutes. The post-fire changes in solute concentrations were generally similar for both catchments and the increase in solute exports was largely a result of greater discharge after the fire and harvesting compared to the burnt eucalypt catchment. The post-fire loss of particulate P in suspended sediment and bedload from the pine catchment for the study period was estimated at a minimum of 11 kg ha −1 and together with the estimated loss of P from burning and the removal of the pines represented approximately 6% of the total P in surface soil and fertilizer applied to the plantation.

Runoff generation in small catchments under a native rain forest and a rubber plantation in Xishuangbanna, southwestern China

AbstractFor the purpose of assessing the potential influence of tropical rain forest conversion to rubber plantation on catchment hydrology, a stable oxygen isotope was used as a tracer to identify the event water and prestorm water components of storm runoff during low‐ and high‐flow conditions in a native tropical rain forest catchment (TRFC) and an artificial rubber plantation catchment (ARPC) in SW China. Isotopic hydrograph separations for the storm of April and September 2004 reveal that the event water made up only a small proportion of discharge (29 and 31%, respectively) at peak flow in the TRFC, while it made up the dominant component at peak flow (62 and 69%, respectively) in the ARPC. The analyses suggest that in the ARPC, the universal presence of compacted terraced tracks associated with land management would encourage infiltration‐excess overland flow. This isotopic investigation demonstrates that tropical rain forest conversion to rubber plantation would markedly change the runoff generation processes in this area.

Forest impact on floods due to extreme rainfall and snowmelt in four Latin American environments 1: Field data analysis

Summary Flood peak data for focus catchments in Costa Rica, Ecuador, Chile and Argentina are analyzed to test the hypothesis that, as the size of the hydrological event increases, the effect of forest cover on the peak discharge becomes less important. Previous research suggests that this hypothesis may hold for small catchments (less than 1 km2) but the pattern is less clear for large catchments. The principal study results are for small paired catchments (0.6–10 km2) with different forest covers (forest/pasture) in highland Ecuador and a small (0.35 km2) plantation catchment in southern Chile subjected to logging. The former were analyzed by comparing the corresponding peak discharges for given rainfall events, the latter by comparing the relationships between peak discharge and rainfall event size for the pre- and post-logging periods. In all cases there is relative or absolute convergence of the responses as discharge increases, with convergence likely for flood return periods of around 10 years. More limited data for larger catchments which have undergone either deforestation or afforestation (131 km2 in Costa Rica and 94–1545 km2 in Chile) suggest that the percentage change in forest cover must exceed 20–30% to provoke a measurable response in peak discharge; convergence of peak discharge response at high flows (return periods of around 5 years) for the different forest covers may then be observed. For a 12.9-km2 snowmelt-affected catchment in Tierra del Fuego, Argentina, extreme floods require rain-on-snow events but the data are not sufficient to quantify the complex relationship between forest cover, event return period and peak discharge. In general, forest cover is unlikely to reduce, significantly, peak discharges generated by extreme rainfall but may still offer substantial mitigation benefits for moderate (i.e. more frequent) rainfall events.

Wildfire and salvage harvesting effects on runoff generation and sediment exports from radiata pine and eucalypt forest catchments, south-eastern Australia

This study examined the effect of wildfire and salvage harvesting on runoff generation and sediment exports from three small forest catchments in south-eastern Australia. In 2006, wildfire burnt a radiata pine catchment and two adjacent natural eucalypt forest catchments which formed part of a long-term hydrological research project. Subsequently, only the pine plantation catchment was salvage harvested. The combined effect of fire and salvage harvesting in the pine catchment caused a substantial increase in runoff compared to the burnt eucalypt forest catchments and pre-fire conditions, particularly in response to high intensity, short duration summer storms. Post-fire maximum suspended sediment concentrations from fixed-interval sampling greatly exceeded pre-fire values for both eucalypt and pine catchments, while sediment (suspended and bedload) exported from the pine catchment exceeded each of the eucalypt catchments by a minimum of 180 and 33 times. However, the export increase was probably closer to 320 and 71 times based on a survey of eroded channels in the pine catchment combined with measured post-survey exports. Notably, seven summer storm events accounted for approximately 80% of the pine catchment sediment yield. Hillslope process measurements indicated that the highest runoff velocities occurred in log drag-lines formed by cable harvesting, while soil water repellency was more extensive in the harvested pine catchment than in the adjacent eucalypt catchment. The latter effect probably resulted from higher burn severity in the pines combined with reduced soil moisture due to less shading after harvesting. Runoff modelling indicated that the log drag-lines acted as an extension to the drainage network and increased peak flows at the harvested catchment outlet by 48% for a high intensity summer storm event, while substantial reductions in modelled runoff were achieved through increasing the hillslope surface roughness coefficient. It is recommended that post-fire salvage operations should avoid the formation of log drag-lines when using cable harvest techniques and maximise surface cover to limit increases to runoff, erosion and catchment sediment exports.

Runoff generating processes in adjacent tussock grassland and pine plantation catchments as indicated by mean transit time estimation using tritium

Abstract. The east Otago uplands of New Zealand's South Island have long been studied because of the environmental consequences of converting native tussock grasslands to other land covers, notably forestry and pasture for stock grazing. Early studies showed that afforestation substantially reduced annual water yield, stream peak flows, and 7-day low flows, mainly as a consequence of increased interception. Tritium measurements have indicated that surprisingly old water is present in catchments GH1 and GH2, and the small headwater wetland and catchment (GH5), and contributes strongly to baseflow. The data have been simulated assuming the presence of two types of water in the baseflow, young water from shallow aquifers connecting hillside regolith with the stream, and old water from deep bedrock aquifers, respectively. The mean transit time of the young water is approximately one month, while that of the old water is 25–26 years as revealed by the presence of tritium originating from the bomb-peak in NZ rainfall in late 1960s and early 1970s. Such a long transit time indicates slow release from groundwater reservoirs within the bedrock, which constitute by far the larger of the water stores. Comparison of the results from catchments GH1 (tussock) and GH2 (pine forest) suggests that about equal quantities of water (85 mm/a) are contributed from the deep aquifers in the two catchments, although runoff from the shallow aquifers has been strongly reduced by afforestation in GH2. This study has revealed the presence of a long transit time component of water in runoff in a catchment with crystalline metamorphic bedrock.

Quantifying the impact of forest management practice on the runoff of the surface‐derived suspended sediment using fallout radionuclides

AbstractIn order to quantify the impact of the abandonment of forest management practices on the runoff of surface‐derived suspended sediment at the catchment scale, we compared the relative contributions of surface soil erosion among Japanese cypress plantation catchments with different stand densities and surface coverage in a 4·9‐ha nested catchment. Source fingerprinting of suspended sediments was conducted using the fallout radionuclides Cs‐137 and Pb‐210ex. Eroded material from hillslope plots having different forest conditions and stream bank material were used as surface and subsurface sediment sources, respectively. The nested watershed monitoring of erosional behaviour and particulate runoff of radionuclides demonstrated decreases in the activities of radionuclides at downstream sampling sites. Hence, the scaling effect of catchments and forest conditions can affect the development of the concentration of surface‐derived material in stream water. An indicator of the forest condition, particularly the surface coverage, light condition of the forest floor was quantified. At the catchment of a thinned plantation with dense understory vegetation, all suspended sediment was calculated to be derived only from subsurface erosion. In contrast, at the catchment of a slightly thinned plantation, the highest proportion of surface erosion (67·8 ± 3·7%) was estimated. Therefore, the forest condition, particularly the light condition at the forest floor, which is related to the ground surface coverage, affects the magnitude of surface soil erosion and the particulate runoff of surface soil. It is suggested that forest management can affect the overland flow generation, stability of the surface soil and associated elements, and downstream water quality. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Streamflow response to Pinus plantation harvesting: Canobolas State forest, southeastern Australia

AbstractStreamflows were measured in two Pinus radiata plantation catchments and one native eucalypt forest catchment in Canobolas State forest from 1999 to 2007. In 2002/2003, clearfall harvesting of 43·2 and 40·3% of two plantation catchments occurred, respectively. Water yields increased by 54 mm (52%), 71 mm (35%) and 50 mm (19%) in the first three years post‐harvest in treated catchment A and by 103 mm (118%), 157 mm (82%) and 119 mm (48%) in treated catchment B relative to the native forest control catchment. In the fourth post‐harvest water year annual rainfall was only 488 mm, which resulted in negligible run‐off in all catchments, regardless of forest cover. In both plantation catchments, monthly streamflows increased significantly (p = 0·01, p &lt; 0·001) due to a significant increase in baseflows (p &lt; 0·001) after harvesting. Monthly stormflows were not significantly affected by harvesting. Flow duration curve analyses indicated a variable response between the two plantation catchments. Treated catchment A was converted from an ephemeral stream flowing 42% of the time pre‐harvest to a temporary stream flowing 82% of the time post‐harvest. These changes occurred throughout all seasons of the year but were most pronounced during summer and autumn when baseflows were maintained post‐harvest but were not observed under native forest or mature pine plantations. By contrast, flow duration increased in treated catchment B from 12% of the time pre‐harvest to 38% of the time post‐harvest with the greatest changes measured during the winter and spring months when streamflow would normally occur under native forest conditions. These observations have important implications for the development of models of plantation water use to be utilized in water resource planning in Australia. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Investigating erosion rates within a Japanese cypress plantation using Cs‐137 and Pb‐210ex measurements

In Japan, soil erosion represents an important threat to the longer‐term sustainability of Japanese cypress plantations. Although it has been demonstrated that raindrop impact, rather than sheet or rill/gully erosion, is the dominant process in both sediment detachment and sediment transport at the point or hillslope scale in such plantations, the role of overland flow at the catchment scale has received little attention to date. To confirm the dominant erosion process operating in a Japanese cypress plantation catchment, we predicted the sediment transport capacities of both overland flow, expressed as a function of the upslope contributing area and the local slope gradient, and rainsplash, expressed as a topographic curvature, for 45 sampling points across the catchment. In addition, we compared the predicted values of sediment transport capacity and rainsplash with the erosion rates estimated using Cs‐137 and Pb‐210ex measurements. The results indicated a close correspondence between the local transport capacity of overland flow and the local erosion rates estimated using the radionuclide measurements. In contrast, there was no significant correlation between the topographic curvature and the erosion rates. Furthermore, the average radionuclide inventories for the catchment were much smaller than the local reference inventories, indicating net loss of eroded soil and radionuclides from the catchment. These results suggest that overland flow makes a significant contribution to surface soil erosion even on forested hillslopes. In addition, the results provide a useful demonstration of the potential for using radionuclide measurements to produce independent information on long‐term erosion rates, which can be used for investigating erosion processes and validating erosion models.

Cs-137, Pb-210ex濃度に基づいたヒノキ林流域の浮遊砂生産源の推定

Cs-137, Pb-210ex濃度に基づいたヒノキ林流域の浮遊砂生産源の推定