Wet depositions of cations in forests across NADP, EMEP, and EANET monitoring networks over the last two decades.

Studies focused on emissions and acid deposition of sulfur (S) and nitrogen (N) and the consequent precipitation acidity have a long history. However, atmospheric depositions of cations play a critical role in buffering precipitation acidity, and providing cationic nutrients for vegetation growth lacks sufficient studies equally. The spatiotemporal patterns of cation depositions and their neutralization potential across broad scales remain unclear. Through synthesizing the long-term data in forest sites (n = 128) derived from three monitoring networks (NADP in Northern America, EMEP in Europe, and EANET in East Asia) on wet deposition of cations (Na+, NH4-N, K+, Mg2+, and Ca2+), this study assesses the temporal changes and spatial patterns of cation depositions and their neutralization potential over the last two decades. The results showed that the depositions of cationic nutrients were considerably higher in EANET compared to NADP and EMEP. The depositions of sea salt-associated sodium exhibited a significant transition from marine (> 15 kg ha-1 year-1) to inland (< 3.0 kg ha-1 year-1) forest sites attributable to the precipitation quantity and influences of sea spray. The higher emissions of NH3 and particulate matter in East Asia explained the higher cation depositions in EANET than NADP and EMEP. The annual trends of cations revealed that only 20-30% of the forest sites showed significant changing trends and the sites widely spread across the three networks. Possibly, base cation (BC) deposition has reached a low and stable condition in NADP and EMEP, while it has high spatial heterogeneity in the temporal change in EANET. The difference in BC deposition among the three networks reflects their distinct development of economy. Our synthesis indicates that the annual trends of neutralization factor (NF) in NADP can be explained by the declining of acid potential (AP), not by neutralization potential (NP) as BC deposition has been stably low over the past two decades. Whereas, the concurrent decreases of AP and NP in EMEP or plateau period of both AP and NP in EANET have come to a standstill of acid neutralizing capacity.

Changes of precipitation acidity related to sulfur and nitrogen deposition in forests across three continents in north hemisphere over last two decades.

Through synthesizing bulk precipitation chemistry in forest sites (n = 128) from three monitoring networks, (NADP in Northern America, EMEP in Europe, and EANET in East Asia), this study quantifies the temporal changes of precipitation acidity and its dominant acidifying agents over the last two decades. Results show distinct declines of sulfate and nitrate depositions and increases of precipitation pH in northeast America and central and east Europe, but not in Asia during 1999 and 2018. The decreases of sulfate and nitrate depositions likely reflect the long-term effort of pollutant emission controls. The temporal pattern of sulfate (SO42-)/nitrate (NO3-) and ammonium nitrogen (NH4-N)/nitrate nitrogen (NO3-N) equivalent ratios indicate that acid rain in the NADP and EMEP have transitioned from sulfate-dominated to nitrate-dominated, and the DIN deposition has shifted from nitrate-dominated to ammonium-dominated in recent years, owing to reductions of sulfur dioxides (SO2) and nitrogen oxides (NOx) emissions. In contrast, sulfate still plays a dominant role on the acidity of precipitation than nitrate in Asia, and NH4-N deposition also has a significant contribution in N flux due to increasing trends of ammonia emissions in Southeast Asia.

Badland landscape response to individual geomorphic events.

Landscapes form by the erosion and deposition of sediment, driven by tectonic and climatic forcing. The principal geomorphic processes of badland - landsliding, debris flow and runoff erosion - are similar to those in full scale mountain topography, but operate faster. Here, we show that in the badlands of SW Taiwan, individual rainfall events cause quantifiable landscape change, distinct for the type of rainfall. Typhoon rain reduced hillslope gradients, while lower-intensity precipitation either steepened or flattened the landscape, depending on its initial topography. The steep topography observed in our first survey is inconsistent with the effects of any of the rainfall events. We suggest that it is due to the 2016 Mw 6.4 Meinong earthquake. The observed pattern in the badlands was mirrored in the response of the Taiwan mountain topography to typhoon Morakot in 2009, confirming that badlands offer special opportunities to quantify natural landscape dynamics on observational time scales.

Constraining tectonic uplift and advection from the main drainage divide of a mountain belt.

One of the most conspicuous features of a mountain belt is the main drainage divide. Divide location is influenced by a number of parameters, including tectonic uplift and horizontal advection. Thus, the topography of mountain belts can be used as an archive to extract tectonic information. Here we combine numerical landscape evolution modelling and analytical solutions to demonstrate that mountain asymmetry, determined by the location of the main drainage divide, increases with increasing uplift gradient and advection velocity. Then, we provide a conceptual framework to constrain the present or previous tectonic uplift and advection of a mountain belt from the location and migration direction of its main drainage divide. Furthermore, we apply our model to Wula Shan horst, Northeastern Sicily, and Southern Taiwan.