Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ18O and δ2H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ18O and δ2H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ18O and δ2H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ18O and δ2H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ18O and δ2H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ18O, δ2H) data have been identified: (1) data plotting along LMWLs for all precipitation at >1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at <1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation.

Evaluation of WRF Model Forecasts and Their Use for Hydroclimate Monitoring over Southern South America

Weather forecasting and monitoring systems based on regional models are becoming increasingly relevant for decision support in agriculture and water management. This work evaluates the predictive and monitoring capabilities of a system based on WRF Model simulations at 15-km grid spacing over the La Plata basin (LPB) in southern South America, where agriculture and water resources are essential. The model’s skill up to a lead time of 7 days is evaluated with daily precipitation and 2-m temperature in situ observations for the 2-yr period from 1 August 2012 to 31 July 2014. Results show high prediction performance with 7-day lead time throughout the domain and particularly over LPB, where about 70% of rain and no-rain days are correctly predicted. Also, the probability of detection of rain days is above 80% in humid regions. Temperature observations and forecasts are highly correlated (r &gt; 0.80) while mean absolute errors, even at the maximum lead time, remain below 2.7°C for minimum and mean temperatures and below 3.7°C for maximum temperatures. The usefulness of WRF products for hydroclimate monitoring was tested for an unprecedented drought in southern Brazil and for a slightly above normal precipitation season in northeastern Argentina. In both cases the model products reproduce the observed precipitation conditions with consistent impacts on soil moisture, evapotranspiration, and runoff. This evaluation validates the model’s usefulness for forecasting weather up to 1 week in advance and for monitoring climate conditions in real time. The scores suggest that the forecast lead time can be extended into a second week, while bias correction methods can reduce some of the systematic errors.

20-Year Climatology ofNO3 −andNH4 +Wet Deposition at Ny-Ålesund, Svalbard

A 20-year dataset of weekly precipitation observations in Ny-Ålesund, Svalbard, was analysed to assess atmospheric wet deposition of nitrogen. Mean annual total nitrogen deposition was 74 mg N/(m2 yr) but exhibited large interannual variability and was dominated by highly episodic “strong” events, probably caused by rapid transport from European sources. The majority (90%) of precipitation samples were defined as “weak” (<2 mg N/m2) and contributed an annual baseline of ~17 mg N/(m2 yr), whereas 10% of precipitation samples were defined as “strong” (>2 mg N/m2) and additionally contributed up to 225 mg N/(m2 yr). Nitrate deposition largely occurred in samples within the solid-precipitation season (16 September–2 June), and ammonium deposition occurred equally in both solid and liquid seasons. Trends of reactive nitrogen emissions from Europe are uncertain, and increasing cyclonic activity over the North Atlantic caused by a changing climate might lead to more strong deposition events in Svalbard.

The Puzzle of Drastic Reduction of Point Source Emissions and Continuing High Deposition of Mercury in Florida

This report shows that the combined emissions of mercury from major point sources of mercury in Florida decreased from about 4.8 short tons in 1994 to 1.3 tons in recent years. A similar reduction of mercury emissions was reported by Florida DEP for south Florida where the Everglades Park is located: Point sources of emissions decreased from a high of 3.4 short tons (3,100 kg) of mercury in 1991 to 0.22 tons (204 kg) in 2000. The Florida DEP study of the Everglades also showed that the mercury concentrations in largemouth bass and in great egret nestlings decreased by a factor of six between 1991 and 2000. On the other hand, our analysis of 330 sets of weekly mercury deposition data, obtained by the Everglades station of the national Mercury Deposition Network (MDN) showed that the annual average deposition in the Everglades did not change significantly from December 1995 to January 2004. Two other interesting findings were that 73% of the total mercury deposition during those eight years occurred in the high precipitation season, between May and October; and that 40% of the weekly samples taken during this eight-year period represented only 3.8 % of the recorded total deposition of mercury. This paper examines the reasons why the substantial decrease of local and regional point sources of mercury emission has not affected substantially the local deposition rates. A likely answer is that climatic conditions in Florida, associated mainly with the warmer months and higher rates of precipitation and evaporation, have a large effect on a) re-emission of previously deposited mercury and b) co-precipitation of global mercury from the atmosphere. This may also explain why Florida, where the present annual rate of mercury emissions from coal-fired power plants (in kilograms per square kilometer) is one fifth that of Pennsylvania, has mercury deposition rates that are twice those reported by MDN for Pennsylvania.