Abstract:A physics-based model is provided for predicting the impact of climate change on stream temperature and, in turn, on Formosan landlocked salmon (Oncorhynchus masou formosanus) habitat. Because upstream watersheds on Taiwan Island are surrounded with high and steep mountains, the influence of mountain shading on solar radiation and longwave radiation is taken into account by using a digital elevation model. Projections using CGCM2 and HADCM3 models and CCCM and GISS models provided information on future climatic conditions. The results indicate that annual average stream temperatures may rise by 0Ð5°C (HADCM3 short term) to 2Ð9°C (CGCM2 long term) due to climate change. The simulation results also indicate that the average suitable habitat for the Formosan landlocked salmon may decline by 333 m (HADCM3 short term) to 1633 m (CGCM2 long term) and 166 m (HADCM3 short term) to 1833 m (CGCM2 long term) depending on which thermal criterion (17°C and 18°C respectively) is applied. The results of this study draw attention to the tasks of Formosan landlocked salmon conservation agencies, not only with regard to restoration plans of the local environment, but also to the mitigation strategies to global climate change that are necessary and require further research.

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Lu H.-Y. (2014): Characterization of extractable metals from the aquifers with arsenic contamination in the Tsengwen Creek, Taiwan. Soil & Water Res., 9: 66-76. Arsenic contamination in groundwater is a common groundwater problem worldwide. To manage groundwater resources effectively, it is crucial to determine the arsenic source. Taiwan's Tsengwen Creek watershed is one of the known areas for groundwater arsenic contamination. Water-rock interactions are evaluated on a regional scale. A conceptual hydrogeological framework is first established based on groundwater hydrochemistry. The local aquifer system can be categorized into high-arsenic deep aquifer and low-arsenic shallow aquifer. The average geochemistry of sediments indicates that arsenic and heavy metals are not significantly enriched in the deeper aquifer on the scale of the whole watershed. Therefore, arsenic contamination in the deeper groundwater of the Tsengwen Creek watershed is not simply source-controlled. However, the Fe-Mn oxides in sediments contain slightly more arsenic in the deep aquifer. The long residence time of groundwater could magnify the enrichment and cause natural arsenic contamination in the deep aquifer.

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Climate change and variability have significant influences on hydrological cycles and the availability of water in the Horn of Africa. Projections of six General Circulation Models (GCMs) in association with high (A2) and low (B1) emission scenarios were adopted in this study from the Special Report on Emission Scenarios (SRES) for the period 2020 -2039 to assess the impacts of climate changes on the Gilgel Abbay and Gumara watershed hydrology, the upper Blue Nile basin, Ethiopia. The GCMs selected were screened in accordance with baseline climate statistics of study areas. A weather generator was employed to generate daily temperature and precipitation to drive the General Water Loading Function (GWLF) hydrological model for simulating runoffs. Projected changes in temperature differences and precipitation ratios relative to the baseline were analyzed to explain the variations in evapotranspiration and the influences on runoff. Despite the fact that the projected magnitude varies among GCMs, increasing runoff in both wet and dry seasons was observed for both watersheds, attributable mainly to the increase in precipitation projected by most GCMs. In contrast to the great increases in runoff, variations in evapotranspiration are less significant. The projected runoff in both watersheds implies increased potential for promoting agricultural irrigation in the dry season. Furthermore, it would allow greater inflow to Lake Tana, the largest contributor to the Ethiopian Renaissance Dam on the Blue Nile. Therefore, concerned local, state, and federal government organizations shall be prepared to harness opportunities from the projected increase in runoff.

Hydrological assessment is critical to the successful implementation of adaption measures. In this study, projections of seven global circulation models (GCMs) associated with high and medium-low Representative Concentration Pathways (RCP 8.5 and RCP 4.5) for the period 2021-2040 and 2081-2100 were adopted to assess changes on runoffs in the Gilgel Abbay watershed, the upper Blue Nile basin. A weather generator was employed to generate daily temperature and precipitation to drive a hydrological model for impact assessment. Despite the projected magnitude of changes varied among different GCMs and RCPs, increasing runoffs in wet-season and decreasing in dry-season are observed in both periods, mainly attributed to the change in projected precipitation. Such changes are profound in cases of RCP 8.5 with respect to those of RCP 4.5 and in cases of 2081-2100 with respect to those of 2021-2040. Although the increasing runoffs would provide greater inflow to Lake Tana, the increase of precipitation in wet-season would imply a higher possibility of flash floods. On the other hand, decrease runoffs in dry-season further intensify existing shortage of irrigation water demand. These changes will have deleterious consequences on the economic wellbeing of the country and require successful implementation of adaption measures to reduce vulnerability.

Oceania rivers are hotspots of DIN (dissolved inorganic nitrogen) and DIP (dissolved inorganic phosphorus) transport due to humid/warm climate, typhoon-induced episodic rainfall and high tectonic activity that create an environment favorable for high/rapid runoff and soil erosion. In spite of its uniqueness, effects of hydrologic controls and land use on the transport behaviors of DIN and DIP are rarely documented. A 2 yr monitoring study for DIN and DIP from three headwater catchments with different cultivation gradient (0 To 8.9%) was implemented during a ~ 3 day interval with an additional monitoring campaign at a 3 h interval during typhoon periods. Results showed the DIN yields in the pristine, moderately cultivated (2.7%), and intensively cultivated (8.9%) watersheds were 8.3, 26, and 37 kg N ha⁻¹ yr⁻¹, respectively. For the DIP yields, they were 0.36, 0.35, and 0.56 kg P ha⁻¹ yr⁻¹, respectively. Higher year-round DIN concentrations and five times larger in DIN yields in intensively cultivated watersheds indicate DIN is more sensitive to land use changes. The high background DIN yield from the relatively pristine watershed was likely due to high atmospheric nitrogen deposition and large subterranean N pool. The correlations between runoff and concentration reveals that typhoon floods purge out more DIN from the subterranean reservoir, i.e., soil, by contrast, runoff washes off surface soil resulting in higher suspended sediment with higher DIP. Collectively, typhoon runoff contributes 20–70% and 47–80%, respectively, to the annual DIN and DIP exports. The DIN yield to DIP yield ratio varied from 97 to 410, which is higher than the global mean of ~ 18. Such a high ratio indicates a P-limiting condition in stream and the downstream aquatic environment. Based on our field observation, we constructed a conceptual model illustrating different remobilization mechanisms for DIN and DIP from headwaters in a mountainous river, which is analogous to typical Oceania rivers and the headwater of large rivers in similar climate zones. Our study advanced our understanding about the role of cyclones, which exert hydrological control, and land use on nutrient export in the Oceania region, benefiting watershed management under the context of climate change