Seminaaripäivä oli mielenkiintoinen ja opettavainen. Oli ilo huomata, että myös muilla ryhmillä oli erittäin kiinnostavia aiheita ja niihin oli selvästi paneuduttu. Esitykset olivat tosin valitettavan lyhyitä eikä niistä saanut kovin kattavaa kuvaa. Pidempi esitysaika ja seminaarien jakaminen kahdelle päivälle olisi ollut siis toivottavaa. Jonkin verran ilmeni päällekkäisyyksiä kosteikko-esityksen kanssa, mutta ne saatiin onneksi karsittua hyvin esityksen aikana.
Kurssista tässä vaiheessa sen verran, että rakenne voisi olla paremmin hallittu/tehokkaampi. Projektityön roolia olisi mukavaa korostaa ja tentti mahdollisesti jättää kokonaan pois. Projektityöhön voisi näin ollen käyttää enemmän aikaa ja etenkin blogin/oppimispäiväkirjan tekemisestä tulisi ehkä myös samalla mielekkäämpää. Projektityö oli tähän asti opettavaisin työ, jota olen kursseilla tehnyt (t.Sanna). Tuli tutkittua hyvin laajasti erilaisia hulevesiartikkeleita ja tiedonhausta oppi paljon lisää. Myös kasvillisuus ja mikrobitoiminta vesiympäristöissä tulivat nopeasti hyvin tutuiksi (t.Sanna). Samalla oppi myös lukemaan erilaisia kaavoituksia ja karttoja. Työ oli mielekästä, sillä aihepiiri oli niin vapaa, että aiheesta sai tehtyä omanlaisensa ja omaa ryhmää kiinnostavan kokonaisuuden, jossa kaikki pääsivät työskentelemään itseä kiinnostavilla osa-alueilla. Tämänkin vuoksi olisi mukavaa, jos projekti olisi kurssin keskeinen ja merkittävin työ. Näin projektiin voisi paneutua syvemmin ja esitysajan pidentyessä olisi mahdollista avata tehtyä työtä enemmän muille kurssin osallistujille. Erittäin positiivista oli ryhmälle määrätty tuutori. Suvi oli todella tärkeä projektin onnistumisen kannalta ja osasi neuvoa meitä epätoivon hetkillä. Tuutorointi oli ehdottoman iso plussa.
Mielestämme onnistuimme hyvin kiteyttämään hulevesisuunnittelun kulmakivet ja tekemään jopa varteenotettavia ehdotuksia. Saimme työskenneltyä tehokkaasti ryhmänä ja kaikki sujui muutamaa tiedonhaku-ongelmaa lukuunottamatta mutkitta.
Loppuun vielä selvitystä muutamasta lähteestä kasvillisuudesta ja viherkatoista.
”Some of these trapped pollutants can then be chemically or biologically degraded or transformed in to the bioretention system. A study conducted by Hong et al. (2006) demonstrated that a 3 cm thick layer of leaf compost mulch efficiently removed 80–95% of all motor oil (30.8 mg L−1) and grease (naphthalene, 1.6 mg L−1; toluene, 2.7 mg L−1) contaminants from synthetic runoff via filtration and sorption. Runoff was applied to the mulch surface at 40 mm h−1 over 6 h. Subsequently, approximately 90% of the dissolved naphthalene, toluene, oil and particulate-associated naphthalene were biodegraded within approximately 3, 4, 8 and 2 days after the event, respectively. Efficiency of contaminant biodegradation was achieved by sorption within the mulch layer coupled with gradual increases in the populations of heterotrophic bacteria and naphthalene-degrading bacteria.”
Vegetation may contribute to pollutant treatment efficiency within bioretention systems both directly and indirectly. Direct benefits occur by degradation of organic pollutants, uptake of macronutrients and heavy metals and maintenance of longer term soil porosity. Indirect effects include influences on soil microbial communities via inputs of organic substrate and by changing the runoff flow between storm events (Read et al., 2008). Vegetation can be strategically employed to divert and slow surface flow and to filter sediments, significantly increasing the physical trapping and biological uptake of nutrients (Davis et al., 2009).
Plants can regulate the movement of pollutants through leaching and surface runoff by controlling the flow of water in soils (Bolan et al., 2011). As plants grow, the evapotranspiration activity of the plants and soil surface reduces the moisture content of the soil layer following inundation, effectively creating a “biopump” (Bolan et al., 2011). By trapping and utilizing water in the root zone, less water is able to transport pollutants beyond the root zone and leach out of the system (Clothier and Green, 1997). Plant growth and death also plays an important role in maintaining the structure and hydraulic conductivity of the media. Active root growth results in macropore formation and maintenance, an important function in reducing clogging of the soil media (Wong, 2006).
Phytoremediation processes may also prove beneficial in the breakdown of C and nutrient-based pollutants and in the uptake of nonbiodegradable pollutants such as metals (Dietz and Claussen, 2006). While not as high as nutrient removal, the metal uptake by plants in bioretention systems has been shown to be up to 10% of the total metal removal (Davis et al., 2001b; Muthanna et al., 2007b).
Plants can immobilize metals in soils by affecting changes in the rhizosphere, which has distinct physical, chemical, and biological conditions. Plant root exudates include a variety of soluble substances such as organic acids that may influence metal dynamics via their effect on acidification, chelation and complexation, precipitation, redox reactions, microbial activity, rhizosphere physical properties, and root morphology (Bolan et al., 2011).
Changes in soil pH are influenced by fluxes in hydroxide (OH−)/H+ ion activity that in turn are related to the differential uptake of cations and anions by plant roots (Tang and Rengel, 2003). The uptake of NH4+, for instance, is counterbalanced by the release of H+ ions of equivalent net charge thereby decreasing rhizosphere pH (Bolan et al., 2011). Apart from this, N transformation and NO3− leaching have been suggested to be major causes of soil acidification (Bolan and Hedley, 2003). Acidification can affect the solubility and speciation of metal ions by (1) modification of surface charge in variable charge soils, (2) altering the speciation of metals, and (3) influencing the redox reactions of the metals (Adriano, 2001). Increased soil acidity (or decreasing pH) generally leads to a decrease in metal adsorption (Tiller, 1989). Naidu et al. (1994) attribute this to three possible reasons. First, in variable charge soils, a decrease in pH causes a decrease in surface negative charge (i.e. cation-exchange capacity) resulting in lower cation adsorption. Second, a decrease in soil pH is likely to decrease hydroxy species of metal cations which are adsorbed preferentially over metal cation. And third, acidification increases dissolution of metal compounds that increases their concentration in soil solution.
Plant root exudates influence the structure and function of microbial assemblages, which in turn mediate the various biochemical transformations in the root zone, including chemical speciation and redox reactions (Park et al., 2011). Redox reactions, both biotic and abiotic, are important in controlling the oxidation state and thus, the mobility and the toxicity of many metals such as Cr, Se, Pb, As, Ni and Cu (Violante et al., 2010). Microbial reduction of certain metals to a lower redox state may result in reduced mobility and toxicity. In addition, microbes produce a number of extracellular metabolites that can complex metals in solution, including polysaccharides, pigments, siderophores and organic acids (Violante et al., 2010). The cell wall of microbes also plays a major role in metal adsorption/reduction as metals are adsorbed by various functional groups of the cell wall, including phosphate, carboxyl, amine as well as phosphodiester groups (Park et al., 2011).
In addition to metal removal, numerous studies have found that vegetated bioretention systems remove more nutrients than nonvegetated systems (Hatt et al., 2007b; Henderson et al., 2007; Lucas and Greenway, 2008). For the removal of N, the type of vegetation has been found to have a critical influence (Bratières et al., 2008; Read et al., 2008). Read et al. (2008) suggest variation in the pollutant removal per root mass between plant species is due to different root architecture and physiology that in turn affects soil physiochemistry and associated microbial communities. The enhanced uptake and assimilation of nutrients, particularly N, in vegetated bioretention systems could be attributed to higher microbial activity and larger microbial populations in the rhizosphere (Henderson et al., 2007; Read et al., 2008). Vegetation may offer a more labile C source to microbes that stimulate microbial mineralization and immobilization and may also be important in creating anaerobic microsites that support denitrification.
Although plant demand for P is generally low, the presence of vegetation has been shown to increase P retention in bioretention system studies (Lucas and Greenway, 2008; Read et al., 2008). Plants and microbes may successfully obtain a greater percentage of P relative to that portion sorbed to soils by taking it up more rapidly, especially in low-sorbing bioretention filter media and in the presence of mycorrhizal fungi (Bolan, 1991; Richardson et al., 2005). Although microbes compete more effectively than plants for nutrients in the rhizosphere, in the long term, plant roots are more successful in removing nutrients because of the longer lifespan of their tissues and their ability to store and translocate greater amounts of nutrients (Kaye and Hart, 1997). The longer lifespan of plants gives vegetation the ability to function as a nutrient and heavy metal sink over time and it has been suggested that the harvesting of bioretention system vegetation can be used as a permanent P and heavy metal removal mechanism (Davis et al., 2006; Hsieh et al., 2007a; Muthanna et al., 2007b).
”Viherkattojen avulla voidaan vähentää muodostuvan huleveden määrää.
Viherkatto myös suojaa kattoa tehokkaasti auringon lämmöltä ja UV-säteilyltä vähentäen jäähdytystarvetta ja pidentäen vesieristeen elinkaarta. Kevyimmillään ja yksinkertaisimmillaan viherkatto voidaan toteuttaa sammal-maksaruohokattona, jonka kasvualusta on vain 5 cm paksuinen ja joka ei vaadi erityistä kunnossapitoa. Tällaisen ohuen sammal-maksaruohokatteen paino märkänä on noin 50 kg/m2, mikä vastaa jokseenkin betonitiilikaton painoa. Katolle on mahdollista toteuttaa paksumman kasvualustan avulla myös istutuksia, jos kattorakenteet toteutetaan riittävän vahvoina. Vuositasolla viherkattojen on arvioitu pidättävän keskimäärin 50 % kokonaissadannasta. Yksittäisessä sadetapahtumassa kattoon pidättyvän veden määrä vaihtelee riippuen mm. sademäärästä, katon kasvualustan paksuudesta ja viherkaton märkyydestä ennen sadetta.”
Sammalet hulevesien hallinnassa:
”Plant-based stormwater management systems such as green roofs are typically composed exclusively of vascular plants. Yet, mosses have several desirable properties that could warrant their more widespread use in green roof applications. In natural systems mosses are important primary colonizers of bare ground, and their establishment improves water storage and provides numerous soil benefits including carbon and nitrogen sequestration. Additionally, mosses often facilitate the establishment and survival of vascular plants at otherwise environmentally harsh or stressful sites. Despite their potential value, few studies have investigated the functional performance of mosses on green roofs.
In this study we evaluated the establishment success and potential stormwater performance of three candidate moss species. We also directly compared the runoff and thermal characteristics of replicate moss covered green roofs to vascular planted and bare roofs. Candidate mosses had high water holding capacities, storing 8–10 times their weight in water compared to only 1.3 times for typical green roof medium. Mock-up roof sections composed of mosses and medium had delayed and reduced runoff flows relative to medium only sections, although the magnitude of these effects varied with moss species. In field trials all three mosses survived a harsh rooftop environment with limited summer irrigation, although lateral growth after one year was minimal. Green roofs planted solely with Racomitrium canescens had between 12–24% higher stormwater retention than vascular or medium only roofs. Moss cover also ameliorated temperature fluctuations on green roofs. Hourly heating rates were buffered to a similar degree (less than half that of surface temperatures) 5 cm below the surface of both moss covered and medium only roofs. In contrast, cooling under the surface of the moss roof was nearly 6 times faster than under the medium only roof. These results demonstrate the potential for mosses to be valuable components of green roofs, either in combination with vascular plants or planted exclusively.
Our results indicate that a relatively thin layer of moss can hold an amount of water comparable to a much thicker layer of extensive medium. Systems composed of moss mats alone or with only a thin underlying medium layer could provide the same stormwater performance as more typical extensive designs. Based on the water holding capacities measured in this study, a roof covered in a mat of R. canescens without any medium could hold 47 L*m-2 at field capacity compared to 33 L*m-2 for a roof covered in a 2.5 cm deep layer of medium. Using moss mats with little or no medium could be a solution for sites where it is impractical to transport and install large amounts of medium, where slopes are too steep to retain medium, or where structural constraints limit the weight capacity of the roof. Such is the case in many potential residential applications. A house with a 140 m2 moss only roof could hold 6,580 L of water at field capacity. Moss covered green roofs also outperformed vascular only roofs in this study, retaining up to 23% more water then vascular and medium only roofs during the winter rain season. Interestingly, the moss roofs performed best under the steady and low intensity natural rain event, which is a typical rain pattern for the Pacific Northwest.
Similar to previous studies (VanWoert et al.2005) we found no significant differences in water retention between the vascular and medium only roofs. This likely reflects both the short duration of this study and the fact that trials took place during the dormancy period of many of the plant species on the vascular roof. Combining winter active mosses with summer active vascular plants could provide complimentary retention and evapotranspiration patterns that would improve stormwater performance over the course of an entire year (Dunnet & Kingsbury 2008).
The results of this study suggest that mosses can significantly enhance the stormwater management performance and thermal environment of green roofs. In addition, lack of roots and high drought tolerance make many mosses well suited for extensive green roof applications, particularly in seasonally dry environments. However, moss species vary in their particular performance related traits. Of the three species tested in this study R.canescens provided the greatest benefits in water retention, holding 10 times its weight in water, and providing the greatest reduction of peak runoff flow. More work is needed to quantify performance characteristics for a wider range of moss species. In addition more research is needed to understand how mosses can be integrated with vascular plants to enhance overall green roof performance. Finally mosses have been shown to have numerous other benefits including mutualistic relationships with vascular plants and sequestration of carbon, nitrogen, and organic matter (Kimmerer 2003; Chiaffredo & Denayer 2004). All of these are yet to be quantified on green roofs, making mosses rife for further study.”
”In addition to rising CO2, a number of other factors, both environmental and biotic, could cause the observed increase in forest water-use efficiency. These include: climate change; nitrogen deposition and accumulation; changes in leaf area, canopy height, surface roughness and the coupling of the canopy to the atmosphere; and long-term instrument drift.
The observed increase in water-use efficiency documented here has a range of important implications for ecosystem function, services and feedbacks to the climate system. These include enhanced timber yields10, improved water availability (which could partially offset the effects of future droughts), and changes in competitive interactions23. Ee directly affects the surface energy balance. Reduced Ee due to higher water-use efficiency24 could therefore lead to higher air temperatures25, decreased humidity, and decreased recycling of continental precipitation26. This would give rise to increased continental freshwater runoff26, along with drought in parts of the world that rely on water transpired in other regions27. Increases in Wei may account for reports of global increases in photosynthesis28, forest growth rates6, 7, 8, and carbon uptake9. Our analysis suggests that rising atmospheric CO2 is having a direct and unexpectedly strong influence on ecosystem processes and biosphere–atmosphere interactions in temperate and boreal forests. Understanding how increasing CO2 induces shifts in terrestrial carbon uptake and water loss and long-term changes in water-use efficiency is of critical importance for improving our ability to project the future evolution of the Earth system.”
”Plants are expected to respond to rising levels of atmospheric carbon dioxide by using water more efficiently. Direct evidence of this has been obtained from forests, but the size of the effect will prompt debate. Keenan and colleagues report that the water-use efficiency of forest canopies in the Northern Hemisphere (Fig. 1) over the past two decades shows a remarkable upward trend. The trend was consistent, with no decreases at any of the 21 forest sites examined. The rates of increase across all sites were large (averaging about 3% per annum) and highly statistically significant.”
”Our ex situ foliar uptake labeling results clearly indicate that water uptake from melting snow by leaves may be one mechanism by which arctic evergreen species can obtain water while soil water is frozen. The only species showing increased δ2H values after being briefly submerged was C. tetragona ( Fig. 3 ), which has live as well as many years of dead leaves tightly appressed to the stems that can trap and hold water. The live leaves either were not completely dry when samples were placed in the vials or water retained under the live and dead leaves was taken up while the samples were air drying. Foliar uptake is a widespread phenomenon that has been previously
Evergreen tundra plants take up water under snow cover, some via roots, but also likely by foliar uptake. The ability to take up water in the subnivean environment allows evergreen tundra plants to take advantage of mild spring conditions under the snow and replenish carbon lost by winter respiration.”
”— a study conducted in an old-growth, species-rich temperate forest showed that species-specific traits rather than species richness mainly explained the variations in plot-level transpiration (Gebauer et al., 2012).
In the study plantation, we suggest that the selection effect was driven by birch trees: indeed, the basal area of this species was always among the highest in the mixed plots and an increase in δ13C from the monoculture to the mixed plots was only observed for birch trees.”
-Sanna, Julia ja Kuutti