Causes and consequences of tipping points in river delta social-ecological systems.

The sustainability of social-ecological systems within river deltas globally is in question as rapid development and environmental change trigger "negative" or "positive" tipping points depending on actors' perspectives, e.g. regime shift from abundant sediment deposition to sediment shortage, agricultural sustainability to agricultural collapse or shift from rural to urban land use. Using a systematic review of the literature, we show how cascading effects across anthropogenic, ecological, and geophysical processes have triggered numerous tipping points in the governance, hydrological, and land-use management of the world's river deltas. Crossing tipping points had both positive and negative effects that generally enhanced economic development to the detriment of the environment. Assessment of deltas that featured prominently in the review revealed how outcomes of tipping points can inform the long-term trajectory of deltas towards sustainability or collapse. Management of key drivers at the delta scale can trigger positive tipping points to place social-ecological systems on a pathway towards sustainable development.

Effects of Ischemic Reperfusion Injury and Remote Conditioning on Passive Leg Raising-Induced Brachial-Artery Dilation.

OBJECTIVES: Passive leg raising (PLR) has been proposed to assess arterial vasodilator reserve and possibly endothelial function. Since endothelial function is sensitive to ischemic-reperfusion (I-R) injury, we determined the effects of I-R injury and ischemic conditioning on PLR-induced brachial-artery dilation (BAD), i.e. PLR-BAD. METHODS: We induced PLR-BAD before and after ipsilateral arm I-R injury (7.5 min of occlusion) in 20 healthy males aged 29 ± 6 years. The protocol was repeated in combination with remote conditioning stimuli (3 × 30 s of contralateral arm occlusions). RESULTS: PLR resulted in significant BAD (3.85%, p < 0.001) before but not after prolonged ischemia (0.25%, p = 0.38). I-R injury, along with either preischemic or postischemic conditioning restored the PLR-BAD response (before: 3.11%, p < 0.001 and after: 3.74%, p < 0.001). CONCLUSIONS: I-R injury blunts the BAD induced by PLR. Remote pre- and postconditioning restore this response. These findings are similar to those previously reported using hyperemia and ultrasound to assess BAD.