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Previous studies suggested that the grasslands may be carbon sinks or near equilibrium, and they often shift between carbon sources in drought years and carbon sinks in other years. It is important to understand the responses of net ecosystem production (NEP) to various climatic conditions across the U.S. Great Plains grasslands. Based on 15 grassland flux towers, we developed a piecewise regression model and mapped the grassland NEP at 250 m spatial resolution over the Great Plains from 2000 to 2008. The results showed that the Great Plains was a net sink with an averaged annual NEP of 24 ± 14 g C m−2 yr−1, ranging from a low value of 0.3 g C m−2 yr−1 in 2002 to a high value of 47.7 g C m−2 yr−1 in 2005. The regional averaged NEP for the entire Great Plains grasslands was estimated to be 336 Tg C yr−1 from 2000 to 2008. In the 9 year period including 4 dry years, the annual NEP was very variable in both space and time. It appeared that the carbon gains for the Great Plains were more sensitive to droughts in the west than the east. The droughts in 2000, 2002, 2006, and 2008 resulted in increased carbon losses over drought‐affected areas, and the Great Plains grasslands turned into a relatively low sink with NEP values of 15.8, 0.3, 20.1, and 10.2 g C m−2 yr−1 for the 4 years, respectively.

An accurate approach is needed for monitoring, quantifying and understanding surface water variability due to climate change. Separating inter-and intra-annual variances from longer-term shifts in surface water extents due to contemporary climate warming requires repeat measurements spanning a several-decade period.Here, we show that trends developed from multi-date measurements of the extents of more than 15,000 water bodies in central Alaska using Landsat Multispectral Scanner (MSS), Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) data were highly influenced by the quantity and timing of the data. Over the 30-year period from 1979 to 2009, the study area had a net decrease (p < 0.05) in the extents of 3.4% of water bodies whereas 86% of water bodies exhibited no significant change. The Landsat-derived dataset provides an opportunity for additional research assessing the drivers of lake and wetland change in this region.

The Northern Great Plains grasslands respond differently under various climatic conditions; however, there have been no detailed studies investigating the interannual variability in carbon exchange across the entire Northern Great Plains grassland ecosystem. We developed a piecewise regression model to integrate flux tower data with remotely sensed data and mapped the 8-d and 500-m net ecosystem exchange (NEE) for the years from 2000 to 2006. We studied the interannual variability of NEE, characterized the interannual NEE difference in climatically different years, and identified the drought impact on NEE. The results showed that NEE was highly variable in space and time across the 7 yr. Specifically, NEE was consistently low (235 to 32 g C ? m 22 ? yr 21) with an average annual NEE of 22 6 24 g C ? m 22 ? yr 21 and a cumulative flux of 215 g C ? m 22. The Northern Great Plains grassland was a weak source for carbon during 2000-2006 because of frequent droughts, which strongly affected the carbon balance, especially in the Western High Plains and Northwestern Great Plains. Comparison of the NEE map with a drought monitor map confirmed a substantial correlation between drought and carbon dynamics. If drought severity or frequency increases in the future, the Northern Great Plains grasslands may become an even greater carbon source. Resumen Los pastizales de las grandes planicies del norte responden de manera diferente bajo diversas condiciones climáticas; sin embargo, no ha habido ningún estudio en detalle que investigue la variabilidad entre añ os en el intercambio de carbono a través de todo el ecosistema de los pastizales de las grandes planicies del norte. Desarrollamos un modelo de regresión para integrar los datos de la torre de flujo con datos medidos de forma remota y establecer el intercambio de ecosistema neto (NEE) de 8 días y 500-m durante los años del 2000 al 2006. Estudiamos la variabilidad de NEE entre añ os caracterizando las diferencias climáticas entre añ os, e identificando el impacto de sequía en NEE. Los resultados mostraron que NEE fue demasiado variable en espacio y tiempo a través de los 7 añ os. Específicamente, NEE fue constantemente bajo (235 to 32 g C ? m 22 ? yr 21) con un promedio anual NEE de 22 6 24 g C ? m 22 ? yr 21 y una variación acumulada de 215 g C ? m 22. Los pastizales de las planicies del norte fueron una fuente baja de carbono durante los añ os 2000-2006 debido a las sequías frecuentes, que afectan considerablemente el equilibrio de carbono, especialmente en la parte occidental de las altas planicies y en el noroeste de las grandes planicies. Comparación del registro de NEE con un mapa de monitoreo de la sequía confirmó una sustancial correlación entre la sequía y la dinámica del carbono. Si la gravedad o frecuencia de la sequía es aumenta en el futuro, los pastizales de las grandes planicies del norte pueden convertirse en una fuente de carbono aún mayor.