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Ombrotrophic ("cloud-fed"), fromAncient Greek ὄμβρος (ómvros) meaning "rain" and τροφή (trofí) meaning "food"), refers tosoils or vegetation which receive all of their water and nutrients fromprecipitation, rather than from streams or springs. Such environments arehydrologically isolated from the surrounding landscape, and since rain isacidic and very low innutrients, they are home to organisms tolerant of acidic, low-nutrient environments. The vegetation of ombrotrophicpeatlands is oftenbog, dominated bySphagnum mosses. Thehydrology of these environments are directly related to theirclimate, as precipitation is the water and nutrient source, and temperatures dictate how quickly water evaporates from these systems.[1]
Ombrotrophic circumstances may occur even in landscapes composed oflimestone or other nutrient-rich substrates – for example, in high-rainfall areas, limestone boulders may be capped by acidic ombrotrophic bog vegetation.Epiphytic vegetation (plants growing on other plants) is ombrotrophic.
In contrast to ombrotrophic environments,minerotrophic environments are those where the water supply comes mainly from streams or springs. This water has flowed over or through rocks often acquiring dissolved chemicals which raise the nutrient levels and reduce the acidity, which leads to different vegetation such asfen orpoor fen.
In most cases, ombrotrophic bogs are extremely nutrient deficient, relying solely onprecipitation and atmosphericdust for nutrient supply. This deficiency is a key characteristic of these ecosystems. However, while ombrotrophicpeat decomposes slowly, some nutrient release does occur. For example, microelements likezinc (Zn),copper (Cu), andmanganese (Mn) are easily mobilized. Additionally, the presence of more nutrient-demanding species in drainage channels draining ombrotrophic bog areas suggests nutrient removal from these ecosystems.[2]
Vegetation in ombrotrophic bogs is adapted to survive in nutrient-poor conditions, withSphagnum mosses playing a critical role in itsnutrient cycle and retention. The addition of extra nutrients and its effects on vegetation and thecarbon cycle can impact an ombrotrophic bog. Increased atmosphericnitrogen (N) deposition is a major concern in northern ecosystems, which are typically nutrient-limited. Some studies suggest that N deposition may increase ecosystems'carbon dioxide (CO2) sink potential by stimulating plant productivity. High N deposition levels inEurope have led to changes in plant species composition inpeatlands andtundra, with documented increases in vascular plantbiomass and decreases inmoss abundance, particularly the genusSphagnum. This moss is critical in bogs for its ability to absorb and retain moisture and nutrients from the atmosphere, and to retardvascular plant growth, thus contributing tocarbon (C)sequestration. Atmospheric N deposition inNorth America is lower than in Europe. Studies inboreal peatlands inCanada have reported apositive correlation between wet N deposition and C accumulation, but it is unclear whether this pattern would continue under higher N deposition levels. With a warmer and drierclimate, without the effect of N deposition, bog communities in Canada are likely to shift and could become weaker C sinks or even C sources.[3]
Ombrotrophic bogs have also been assessed for their uses as archives of atmosphericmercury deposition. This involves studying thesolid state distributions of mercury and other metals in the bog to understand postdepositional transport processes and the immobility of deposited trace metals. It was found thatmercury (Hg) andlead (Pb) are immobile in ombrotrophic peat, indicating that their distribution can be used to determine temporal changes in deposition and suggesting that ombrotrophic bogs can serve as reliable records of historic atmospheric mercury deposition. Historic atmospheric mercury deposition in Arlberg Bog,Minnesota, increased gradually after the mid-1800s, peaked between 1950 and 1960, and may have declined thereafter.Preindustrial deposition levels were estimated to be about 4 μg/m2 per year, while recent deposition levels were approximately 19 μg/m2 per year. The deposition of mercury in Arlberg Bog appeared to have been influenced by both regional and/or local-scale sources, highlighting the complex nature of atmospheric deposition patterns and the need to consider multiple factors when studyingmetal deposition in ombrotrophic bogs.[4]
However, despite their significance as sources offuel andhorticultural peat moss, there is still much to uncover about theecological andbiogeochemical processes of ombrotrophic bogs. Chemical analyses ofpeat profiles could shed light on this aspect, but the data collected so far have not been adequate for such analysis. One of the main challenges is the infrequent sample intervals and the lack ofchemical data on surface peat or sufficient information onhabitat conditions. Although some nutrient release occurs in ombrotrophic peat, there is a significant gap in understanding the rate and depth of element release and howmobility varies within these ecosystems. Therefore, despite the recognition of their importance, ombrotrophic bogs remain relativelyunderstudied, highlighting the need for further research to fill these knowledge gaps and gain a comprehensive understanding of their ecological processes.[2]
