Thonon Ivo, Klok Chris
Department of Physical Geography, Faculty of Geosciences, University Utrecht, PO Box 80115, 3508 TC Utrecht, The Netherlands.
Sci Total Environ. 2007 Jan 1;372(2-3):585-94. doi: 10.1016/j.scitotenv.2006.10.028. Epub 2006 Nov 30.
River floodplains are dynamic and fertile ecosystems where soil invertebrates such as earthworms can reach high population densities. Earthworms are an important food source for a wide range of organisms including species under conservation such as badgers. Flooding, however, reduces earthworm numbers. Populations recover from cocoons that survive floods. If the period between two floods is too short such that cocoons cannot develop into reproductive adults, populations cannot sustain themselves. Both climate change and floodplain rehabilitation change the flooding frequency affecting earthworm populations. The present paper estimates the influence of climate change and floodplain rehabilitation on the viability of earthworm populations in a Dutch floodplain; the Afferdensche and Deestsche Waarden along the River Waal. This floodplain will be part of major river rehabilitation plans of the Dutch government. In those plans, the floodplain will experience the construction of a secondary channel and the removal of part of its minor embankment. To estimate the impact of these plans and climate change, we used a dataset of daily discharges for 1900-2003 for the River Rhine at the Dutch-German border. We perturbed this dataset to obtain two new datasets under climate change scenarios for 2050 and 2100. From the original and two projected datasets we derived the frequency distributions for the annual periods without inundations for the studied floodplain. We subsequently compared the duration of these inundation-free (dry) periods with the maturation age distribution for L. rubellus as derived from a Dynamic Energy Budget model. This comparison yielded in which parts of our study area and under which climate conditions the populations would still be viable, be able to adapt or become extinct. The results show that climate change has almost no adverse effect on earthworm viability. This is because climate change reduces the flooding frequency during the earthworms growing season. Floodplain rehabilitation, on the other hand, reduces the part of the floodplain area where populations can sustain themselves. Before rehabilitation, only 12% of the floodplain area cannot sustain a viable earthworm population. After rehabilitation, this increases to 59%, 28% of which is due to more frequent flooding. Enhanced exposure to soil contaminants may further suppress earthworm viability. This could frustrate further nature development and the viability of earthworm-dependent species such as the badger (Meles meles) or little owl (Athene noctua vidalli species), which is an objective of the river rehabilitation plans in the Netherlands.
河流洪泛区是动态且肥沃的生态系统，蚯蚓等土壤无脊椎动物在其中能够达到很高的种群密度。蚯蚓是包括獾等受保护物种在内的多种生物的重要食物来源。然而，洪水会减少蚯蚓数量。种群从在洪水中存活下来的茧中恢复。如果两次洪水之间的间隔太短，以至于茧无法发育成有繁殖能力的成虫，种群就无法维持自身。气候变化和洪泛区恢复都会改变洪水发生频率，进而影响蚯蚓种群。本文估计了气候变化和洪泛区恢复对荷兰洪泛区（瓦尔河沿岸的阿费尔登斯和德斯特斯瓦尔德）蚯蚓种群生存能力的影响。这片洪泛区将成为荷兰政府主要河流恢复计划的一部分。在这些计划中，洪泛区将经历一条二级河道的建设以及部分小堤坝的拆除。为了估计这些计划和气候变化的影响，我们使用了荷兰 - 德国边境莱茵河1900 - 2003年每日流量的数据集。我们对该数据集进行扰动，以获得2050年和2100年气候变化情景下的两个新数据集。从原始数据集和两个预测数据集出发，我们得出了所研究洪泛区无淹没年周期的频率分布。随后，我们将这些无淹没（干燥）期的持续时间与从动态能量预算模型得出的红蚯蚓成熟年龄分布进行比较。这种比较得出了在我们研究区域的哪些部分以及在何种气候条件下种群仍能存活、能够适应或灭绝。结果表明，气候变化对蚯蚓的生存能力几乎没有不利影响。这是因为气候变化降低了蚯蚓生长季节的洪水发生频率。另一方面，洪泛区恢复减少了种群能够维持自身的洪泛区面积。恢复之前，只有12%的洪泛区面积无法维持蚯蚓种群存活。恢复之后，这一比例增加到59%，其中28%是由于洪水更加频繁。更多地接触土壤污染物可能会进一步抑制蚯蚓的生存能力。这可能会阻碍进一步的自然发展以及依赖蚯蚓的物种（如獾或小鸮）的生存能力，而这是荷兰河流恢复计划的一个目标。
