Nitrogen and phosphorus budgets were compiled for the littoral (29 km) and pelagic (329 km) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km (area of littoral) yr; net littoral retention is 31% 13% for P and 40% 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A MonteCarlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to 20%), a doubling in P-loading, a drop in lake level of 1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover. A buffering role for the littoral is generally not incorporated explicitly in whole-lake eutrophication studies of large, deep lakes (e.g., Vollenweider 1975; Schindler 2006; Scavia et al. 2014; Beutel and Horne 2018; Fink et al. 2018; but see Sachse et al. 2014). In contrast, studies on shallow lakes take littoral vegetation into account as an important element in nutrient dynamics (e.g., Jeppesen et al. 1999; Søndergaard et al. 2007). This implies that the possibly shifting share of littoral vegetation in whole lake nutrient budgets is ignored, despite Kalff’s (2002, p. 295) suggested that “macrophyte beds ... permit portions of the littoral ... to serve as net sinks.” Perennial charophyte beds, in particular, may have the potential to serve as nutrient sink, as they form dense carpets protecting the sediment from resuspension (Benoy and Kalff 1999; Vermaat et al. 2000), retain assimilated N during slow decomposition of the lower tissue (Rodrigo et al. 2007), and coprecipitate P with carbonates during photosynthesis which is then retained in the sediment (Kufel et al. 2013). Given the importance of light availability for the colonization depth of water plants (Chambers and Kalff 1985; Duarte and Kalff 1990; Schwarz et al. 2002; Søndergaard et al. 2013), its interplay with bathymetry can be expected to determine the extent of submerged vegetation (Kolada 2014; Sachse et al. 2014). Indeed, in many large lakes where macrophytes have declined during eutrophication, load reduction programs have led to increased transparency, reduced plankton stocks, and often a recovery of macrophytes (Jeppesen et al. 2005; Hilt et al. 2010; Mueller et al. 2014). Ancient, large, deep, and oligotrophic Lake Ohrid (shared between Albania and North Macedonia) has not lost its macrophytes, but is considered to be under threat of eutrophication (a.o. Matzinger et al. 2007; Schneider et al. 2014) due to a rapidly expanding urbanization (including tourism) and intensifying agriculture in its catchment. Paradoxically, this is not reflected in the phytoplankton composition of the open pelagic (e.g., Matzinger et al. 2007), though an increasing pelagic P concentration (from a historic 1.3 mg m to a “current” 4.6 mg m) and decreasing deep hypolimnetic *Correspondence: jan.vermaat@nmbu.no This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Additional Supporting Information may be found in the online version of this article.

中文翻译：

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大湖沿岸植被的养分保留：奥赫里德湖能否应对当前和未来的负荷？

为古老、深、清澈和硬水奥赫里德湖（阿尔巴尼亚和北马其顿）的沿岸（29 公里）和远洋（329 公里）编制了氮和磷预算，以评估沿岸在养分保留方面的重要性。P 主要来自国内点源（73%），对于 N，这是岩溶渗流（50%）。沿海总负荷估计为 1700 kg P 和 23,200 kg N km（沿海面积）yr；P 的净沿海保留率为 31% 13%，N 为 40% 16%，主要在密集的轮藻带中。P的保留主要是由于碎屑掩埋，也有由于共沉淀；N 保留是由于碎屑掩埋和反硝化作用。MonteCarlo 合理性分析通过增加非联网家庭投入（从外部负荷的 20% 到 27%）来平衡预算，减少了 27% 的远洋沉积物 P 掩埋和 25% 的沿海反硝化作用。对应于 SRES A2 和 B1 的 2100 年情景预测与 AQUASIM 湖泊生态系统模型相关联。在 B1 下，与现在相比，变化很小。然而，A2导致降水量大幅减少，蒸散量增加，河流流出量减少（至20%），P负荷增加一倍，湖泊水位下降1.5 m，范围下降轮藻带。沿岸的面积负荷会相应增加，但水的透明度不会下降太多。此外，沿海植被将见证物种组成的变化，以及丝状枝藻覆盖率的增加。在大型深湖的全湖富营养化研究中通常没有明确纳入沿海的缓冲作用（例如，沃伦韦德 1975；辛德勒 2006; 斯卡维亚等。2014; Beutel 和 Horne 2018；芬克等人。2018 年；但请参阅 Sachse 等人。2014）。相比之下，浅湖研究将沿海植被视为营养动态中的一个重要因素（例如，Jeppesen 等人，1999 年；Søndergaard 等人，2007 年）。这意味着，尽管 Kalff (2002, p. 295) 建议“大型植物床……允许部分沿海……作为净汇”，但忽略了整个湖泊养分预算中沿海植被可能发生的变化份额。尤其是多年生轮藻床可能有作为养分汇的潜力，因为它们形成致密的地毯，保护沉积物免于再悬浮（Benoy 和 Kalff 1999；Vermaat 等人，2000），在下部组织的缓慢分解过程中保留同化的 N （罗德里戈等人，2007 年），并在光合作用过程中将 P 与碳酸盐共沉淀，然后将其保留在沉积物中（Kufel 等人，2013 年）。考虑到光照对水生植物定植深度的重要性（Chambers 和 Kalff 1985；Duarte 和 Kalff 1990；Schwarz 等人 2002；Søndergaard 等人 2013），它与测深的相互作用可以预期确定淹没的程度植被（Kolada 2014；Sachse 等人，2014）。事实上，在富营养化期间大型植物减少的许多大型湖泊中，减少负荷计划导致透明度增加，浮游生物数量减少，大型植物通常会恢复（Jeppesen 等人，2005 年；Hilt 等人，2010 年；Mueller 等人，2014 年） ）。古老的、大的、深的、贫营养的奥赫里德湖（阿尔巴尼亚和北马其顿共有）并没有失去它的大型植物，但由于快速扩张的城市化（包括旅游业）和集水区的农业集约化，被认为受到富营养化的威胁（ao Matzinger 等人，2007 年；Schneider 等人，2014 年）。矛盾的是，这并没有反映在开阔的中上层浮游植物的组成中（例如 Matzinger 等人，2007 年），尽管中上层磷浓度不断增加（从历史上的 1.3 mg m 到“当前”的 4.6 mg m）并降低了深潜*信件：jan.vermaat@nmbu.no 这是一篇基于知识共享署名-非商业性许可条款的开放获取文章，允许在任何媒体中使用、分发和复制，前提是原始作品被正确引用且未被使用用于商业目的。可以在本文的在线版本中找到其他支持信息。