Effects of Water Table Drawdown on Root Production and Aboveground Biomass in a Boreal Bog

We studied the effect of long-term water table drawdown on the vascular plant community in an ombrotrophic bog in central Finland by measuring aboveground biomass and belowground production (by in-growth cores) across plant functional groups including herbs, shrubs, and trees. We compared drained and undrained portions 45 years after the installation of a drainage ditch network, which has lowered water levels of 15–20 cm on average in the drained part of the site. Although shrub fine root production did not differ significantly between sites, water table drawdown increased belowground tree fine root production by 740% (3.8 ± 5.4 SD and 28.1 ± 24.1 g m^?2 y^?1 in undrained and drained sites, respectively) at the expense of herb root production, which declined 38% (27.62 ± 16.40 and 10.58 ± 15.7 g m^?2 y^?1 in undrained and drained sites, respectively) yielding no significant overall change in total fine root production. Drainage effects on aboveground biomass showed a similar pattern among plant types, as aboveground tree biomass increased dramatically with drainage (79 ± 135 and 2546 ± 1551 g m^?2 in drained and undrained sites, respectively). Although total shrub biomass was not significantly different between sites, shrubs allocated more biomass to stems than leaves in the drained site. Drainage also caused a significant shift in shrub species composition. Although trees dominated the aboveground biomass following water table drawdown, understorey vegetation, mainly shrubs, continued to dominate belowground fine root production, comprising 64% of total root production at the drained site. Aboveground biomass proved to be a good predictor of belowground production, suggesting that allometric relationships can be developed to estimate belowground production in these systems. Increase in tree root production can counteract decrease in herb fine root production following water table drawdown, emphasizing the importance of plant functional type responses to water table drawdown. Whether these changes will offset ecosystem C loss via increased plant C storage or stimulate soil organic matter decomposition via increased above- and belowground litter inputs requires further study.     

The role of containerships as transfer mechanisms of marine biofouling species

Fouling of ships is an important historical and enduring transfer mechanism of marine nonindigenous species (NIS). Although containerships have risen to the forefront of global maritime shipping since the 1950s, few studies have directly sampled fouling communities on their submerged surfaces, and little is known about differences in the fouling characteristics among commercial ship types. Twenty-two in-service containerships at the Port of Oakland (San Francisco Bay, California) were sampled to test the hypothesis that the extent and taxonomic richness of fouling would be low on this type of ship, resulting from relatively fast speeds and short port durations. The data showed that the extent of macroorganisms (invertebrates and algae) was indeed low, especially across the large surface areas of the hull. Less than 1% of the exposed hull was colonized for all apart from one vessel. These ships had submerged surface areas of >7000 m², and fouling coverage on this area was estimated to be <l7 m² per vessel, with zero biota detected on the hulls of many vessels. The outlying smaller vessel (4465 m²) had an estimated coverage of 90% on the hull and also differed substantially from the other ships in terms of its recent voyage history, shorter voyage range and slower speeds. Despite the low extent of fouling, taxonomic richness was high among vessels. Consistent with recent studies, a wide range of organisms were concentrated at more protected and heterogeneous (non-hull) niche areas, including rudders, stern tubes and intake gratings. Green algae and barnacles were most frequently sampled among vessels, but hydroids, bryozoans, bivalves and ascidians were also recorded. One vessel had 20 different species in its fouling assemblage, including non-native species (already established in San Francisco Bay) and mobile species that were not detected in visual surveys. In contrast to other studies, dry dock block areas did not support many organisms, despite little antifouling deterrence in some cases. Comparisons with previous studies suggest that the accumulation of fouling on containerships may be lower than on other ship types (eg bulkers and general cargo vessels), but more data are needed to determine the hierarchy of factors contributing to differences in the extent of macrofouling and non-native species vector risks within the commercial fleet.     

Effect of barnacle fouling on ship resistance and powering

Predictions of added resistance and the effective power of ships were made for varying barnacle fouling conditions. A series of towing tests was carried out using flat plates covered with artificial barnacles. The tests were designed to allow the examination of the effects of barnacle height and percentage coverage on the resistance and effective power of ships. The drag coefficients and roughness function values were evaluated for the flat plates. The roughness effects of the fouling conditions on the ships’ frictional resistances were predicted. Added resistance diagrams were then plotted using these predictions, and powering penalties for these ships were calculated using the diagrams generated. The results indicate that the effect of barnacle size is significant, since a 10% coverage of barnacles each 5 mm in height caused a similar level of added power requirements to a 50% coverage of barnacles each 1.25 mm in height.     

Quantitative exploration of the contribution of settlement,growth, dispersal and grazing to the accumulation of natural marine biofilms on antifouling and fouling-release coatings

The accumulation of microbial biofilms on ships’ hulls negatively affects ship performance and efficiency while also playing a role in the establishment of even more detrimental hard-fouling communities. However, there is little quantitative information on how the accumulation rate of microbial biofilms is impacted by the balance of the rates of cell settlement, in situ production (ie growth), dispersal to surrounding waters and mortality induced by grazers. These rates were quantified on test panels coated with copper-based antifouling (AF) or polymer-based fouling-release (FR) coatings by using phospholipids as molecular proxies for microbial biomass. The results confirmed the accepted modes of efficacy of these two types of coatings. In a more extensive set of experiments with only the FR coatings, it was found that seasonally averaged cellular production rates were 1.5 ± 0.5 times greater than settlement and the dispersal rates were 2.7 ± 0.8 greater than grazing. The results of this study quantitatively describe the dynamic balance of processes leading to the accumulation of microbial biofilm on coatings designed for ships’ hulls.     

Quantifying the extent of niche areas in the global fleet of commercial ships: the potential for “super-hot spots” of biofouling

Niche areas of ships, such as lateral thruster tunnels, sea chests, and propellers, are often hot spots for the accumulation of biofouling organisms, a potential source of aquatic invasive species. Yet, the relative importance of different niche areas is poorly resolved, in terms of both total surface area and the associated biota (i.e., the species of organisms and their abundances). To address this information gap, a method was developed to estimate the extent of various niche areas in the global fleet of 120,252 commercial ships active between 1999 and 2013. The total niche area for these vessels was estimated to be 32,996 × 10³ m², representing approximately 10% of the total wetted surface area (WSA) available for colonization by biota. Considering the portion of niche areas relative to the total WSA, it was highest for passenger vessels (27%), followed by tugs (25%), and fishing vessels (21%), with niche areas representing a small portion of the WSA for bulk carriers and tankers (7–8%). Examining the different types of niche areas, thruster tunnels had the greatest total extent (10,189 × 10³ m²), representing a disproportionately large contribution (>50%) of the total niche area for passenger vessels and tugs compared to other vessel types. This result, combined with the use and cleaning of thrusters, may render them “super-hot spots” of biofouling. The uneven distribution and extent of niche areas across vessels has implications for transfers of organisms and management strategies to reduce invasions associated with the surfaces of ships.     

冬季水鸟对崇明东滩水产养殖塘的利用

自然湿地的丧失和退化给依赖湿地生存的水鸟带来了严重威胁,人工湿地作为水鸟栖息地的功能日益受到关注.水产养殖塘是人工湿地的重要类型之一.通过研究崇明东滩水产养殖塘冬季水鸟群落组成及其栖息地特征,发现大面积养殖塘比小面积养殖塘吸引更多种类和更高密度的水鸟.养殖塘在放水前水位较高时吸引更多游禽栖息,而在放水后水位较低时吸引更多涉禽;在放水过程中,养殖塘中水鸟的种类最多,密度最大.另外,在放水的不同时期,不同的环境因子对水鸟群落的影响不同:放水之前,养殖塘水面面积和平均水深是水鸟种类和数量的主要影响因子,其中游禽种类和数量受水面面积影响较大,涉禽种类和数量受平均水深影响较大;放水过程中,裸地面积、芦苇面积、干扰程度、平均水深和水深变异对水鸟、游禽和涉禽的种类和数量起主要作用;放水之后,水深变异对水鸟种类和数量的影响较大,而影响游禽种类和数量的主要因子是水面面积,影响涉禽种类和数量的主要因子是水深变异.研究表明,通过对影响水鸟栖息地利用的主要因子的有效管理,养殖塘在提供经济效益的同时也能为水鸟提供适宜的栖息地.     

Regulated deficit irrigation in different phenological stages of potted geranium plants: water consumption, water relations and ornamental quality

The irrigation water requirements and sensitivity to water deficits of ornamental plants is of great interest to horticultural producers for planning irrigation strategies. The effect of different deficit irrigation strategies on physiological and morphological parameters in geranium plants was studied in different growth phases to evaluate how such strategies can be safely used and to ascertain whether the flowering phase is sensitive to deficit irrigation. Pelargonium × hortorum L.H. Bailey plants, grown in a controlled growth chamber, were subjected to four irrigation treatments: control (100 % water field capacity throughout the experiment), sustainable deficit irrigation (75 % water field capacity throughout the experiment), and two regulated deficit irrigation treatments that included water stress during the vegetative growth phase or during the flowering development phase. Although the total amount of irrigation water was similar in the three deficit irrigation treatments (around 80 % of the control value), the lowest values for both height and flowering were found when deficit irrigation was applied during flowering. This indicates that plant quality does not only depend on the amount of water applied but also on the time when the reduction is applied, and that flowering is the most sensitive phase to water stress. Evapotranspiration was related to the formation of inflorescences and to increased plant height. When the irrigation strategy was changed, plants increased or decreased their water consumption and stomatal conductance to adjust to the new conditions by regulating stomatal opening, although, in general, the values of both parameters remained below those observed in the control plants.     

Inhibitory effects of drought induced acidification on phenol oxidase activities in Sphagnum-dominated peatland

Extracellular phenol oxidases play an important role in the soil carbon cycle. How phenol oxidase activity in peatlands will respond to increased aeration induced by water-table drawdown or droughts if global warming continues remains unclear. We investigated the short-term effects of drought induced acidification on phenol oxidase activities of a Sphagnum-dominated peatland in central China. The results indicated a significant acidification induced by drought, with a decline in the average pH value from 5.67 ± 0.08 under waterlogging to 4.84 ± 0.08 in droughted peat. In addition, drought-treated peat had a lower average value of phenol oxidase activities compared to the waterlogging-treated peat (mean values of 0.1404 ± 0.0305 and 0.2623 ± 0.0324 μmol diqc min^?1 g^?1, respectively). The decreased phenol oxidase activities were mainly attributed to the acidification induced by drought. However, the declines in phenol oxidase activity did not lead to the reduction of the degradation in the deeper peat. Under drought conditions, a considerable part of the adsorbed phenolics, consisting primarily of high molecular-weight organic substances with phenolic groups, were further degraded into smaller-sized or lower molecular weight hydrophilic fractions in the vicinity of the water table. Our results highlight the important role of the water table position in peat decomposition processes. Even with lower activities of phenol oxidase, the decomposition processes were able to effectively keep on going as long as there was sufficient supply of water, oxygen and nutrients.     

Long-term water table manipulations alter peatland gaseous carbon fluxes in Northern Michigan

Northern peatland water table position is tightly coupled to carbon (C) cycling dynamics and is predicted to change from shifts in temperature and precipitation patterns associated with global climate change. However, it is uncertain how long-term water table alterations will alter C dynamics in northern peatlands because most studies have focused on short-term water table manipulations. The goal of our study was to quantify the effect of long-term water table changes (~80 years) on gaseous C fluxes in a peatland in the Upper Peninsula of Michigan. Chamber methods were utilized to measure ecosystem respiration (ER), gross primary production (GPP), net ecosystem exchange (NEE), and methane (CH₄) fluxes in a peatland experiencing levee induced long-term water table drawdown and impoundment in relation to an unaltered site. Inundation raised water table levels by approximately ~10 cm and resulted in a decrease in ER and GPP, but an increase of CH₄ emissions. Conversely, the drained sites, with water table levels ~15 cm lower, resulted in a significant increase in ER and GPP, but a decrease in CH₄ emissions. However, NEE was not significantly different between the water table treatments. In summary, our data indicates that long-term water table drawdown and inundation was still altering peatland gaseous C fluxes, even after 80 years. In addition, many of the patterns we found were of similar magnitude to those measured in short-term studies, which indicates that short-term studies might be useful for predicting the direction and magnitude of future C changes in peatlands.     

Wave reduction in a mangrove forest dominated by Sonneratia sp.

Based on a field observation at the Vinh Quang coast in northern Vietnam, the characteristics of wave reduction due to the drag force of one mangrove species, Sonneratia sp., were quantitatively analyzed. The reduction rate of sea waves in this area changed substantially with the tidal phase, due to the unique vertical configuration of Sonneratia sp. At the shallow range of water depth, since the shape of pneumatophores of Sonneratia sp. tapers off upward, the effect of drag force by these roots on the wave reduction decreased with the increase in the water level, resulting in a decrease in the rate of wave reduction. On the other hand, when water levels rose above the height of thickly spread branches and leaves of these trees, the rate of wave reduction increased again with an increase in the water level. Further, at this high range of water level, the rate of wave reduction depended strongly on the incident wave height. These results indicate that the thickly grown mangrove leaves effectively dissipate huge wave energy which occurs during storms such as typhoons, and protect coastal areas. Referring to the past studies, our results suggest that the hydrodynamic knowledge in various mangrove conditions such as the vertical configuration of mangrove species, their vegetation conditions, water depth, incident wave condition and the relationships between these factors should be further accumulated and then quantitatively formulated in order to protect coastal areas from severe sea waves.     

Wave-energy distribution and hurricane effects on Margarita Reef,southwestern Puerto Rico

Wave measurements at Margarita Reef in southwestern Puerto Rico show that wave height decreases as waves travel across the forereef and into the backreef. Wave spectra reveal the presence of two wave trains impinging on the reef during the study: trade-wind waves and locally generated seas. Significant wave height calculated from the spectra show an average reduction of 19.5% from 20- to 10-m isobaths and 26% from 20- to 5-m isobaths. The significant wave height decreases an average of 82% for waves traveling across the reef crest and into the backreef. Wave-energy reduction is 35% from 20- to 10-m isobaths and 45% from 20- to 5-m isobaths. Energy loss across the reef crest is 97% which translates into the formation of strong across-the-reef currents capable of moving coarse sediment. Refraction diagrams of waves impinging on the reef from the SE provide a display of wave energy distribution around the reef. The transmission coefficients calculated for trade-wind waves and locally generated seas have means of 18% and 39%, respectively. A wave height model with negligible energy dissipation, produces wave height estimates that are, in general, within the ±15% error bands. Results of wave-energy changes from this study were applied to waves representative of hurricane conditions at the reef. Aerial photographs of the reef before and after the passage of hurricanes were compared to assess the reef changes. Changes observed in the photographs are interpreted as products of sediment transport by hurricane-generated waves. The patterns of change agree with the refraction diagrams suggesting that waves were the main agents of change at margarita Reef during severe storms. Correspondence to: A. Lugo-Fernández}     

Towards minimizing transport of aquatic nuisance species in ballast water: Do organisms in different size classes respond uniformly to biocidal treatment?

To reduce the transport and delivery of aquatic nuisance species in ships’ ballast water and comply with standards for the number of living organisms that may be discharged, biocidal agents and processes, such as chemical dosing, have been repurposed to treat ballast water. We evaluated whether marine planktonic organisms—the typical targets of these biocides—respond in unison to simulated treatment. Organisms were concentrated from seawater, which was amended with dissolved and particulate matter and cultured microalgae, and then treated by chlorination, ultraviolet radiation, or deoxygenation. Living organisms in three size classes (≥50, ≥10 and <50, and <10 µm [represented by culturable, heterotrophic bacteria]) were counted prior to and periodically after treatment. Regardless of whether the differences in concentrations between the control and treatments were significant or insignificant, in general, organisms across the size classes reacted comparably to treatments, with some exceptions in the <10 µm size class. The parallel responses of organisms to treatment—if shown to generalize to other water conditions, assemblages of organisms, and scales of treatment—may justify using a single size class to predict the responses of organisms across the broad size spectra. Notably, because most ballast water management systems employ a filtration step to remove organisms ≥50 µm, if organisms in the ≥10 and <50 µm size class were assessed to determine a vessel’s compliance with the discharge standard, it would be imperative that any filters would be evaluated to ensure they were functioning properly and removed organisms as designed.     

Structural diversity as a habitat indicator for endangered lakeshore flora using an assemblage of common plant species in Atlantic Canada

Vegetation structure, defined by the height, cover, and types of plants, is an important component of habitat suitability for plant species or communities. The identification of potential habitat is a crucial knowledge gap for endangered Atlantic Coastal Plain Flora (ACPF), a group of taxonomically unrelated plants that share common habitat types and are mostly found on lakeshores and wetlands in the Atlantic coastal region of North America. Our objectives were to assess spatial patterns and relationships of ACPF richness and structural diversity indices at different scales and positions along the lakeshore-to-forest gradient. We sampled 16 sites at 7 lakes in southwestern Nova Scotia using contiguous 20 × 20 cm quadrats along 20 m transects, perpendicular to the waterline, and in 5 × 5 m grids, between the lake and the forest edge. We measured the cover of 19 ACPF species and structural elements at different heights and calculated structural diversity indices using the Shannon index. Spatial patterns were assessed using one- and two-dimensional wavelet variance and covariance. The edge of the zone of high ACPF richness coincided with greater structural diversity at the lakeshore edge. Herbaceous ACPF richness was positively associated with structural diversity at finer scales and on lakeshores, but negatively associated at coarser scales and farther from the waterline. A strong association of structural diversity with ACPF richness suggests it could be used as a habitat indicator for ACPF on lakeshores, which could help the identification and conservation of potential suitable shorelines for ACPF populations in Nova Scotia.     

Ecological applications of differences in the hydraulic efficiency of palms and broad-leaved trees

Key message

In tropical forests, co-occurring woody monocot and dicot species adapted different water use strategies highly depending on their investment in the hydraulic conduit properties.

Abstract

We studied the hydraulic efficiency of palms and broad-leaved tropical tree species from a moist tropical lowland forest in the Central Brazilian Amazon. Therefore, we harvested 34 trees and 10 açai palms and measured vessel size and frequency at diameter at breast height and additionally at the base of the crown shaft for the palms. Further, we assessed the active xylem area to estimate the hydraulic conductivity through Hagen Poiseuille’s adapted theoretical equation. Mean vessel diameter in dicot trees was 127.62 ± 49.22 μm with an average 9.09 ± 6.50 vessels per mm². Mean conduits sizes at the base (h = 0.10 m) of palm trees were larger with 288.20 ± 32.96 μm and less frequent with 1.40 ± 0.46 vessels per mm². Hydraulic conductivity was on average 3.31 ± 4.59 kg m^?1 s^?1 MPa^?1 for dicot trees. Mean hydraulic conductivity in açai palms was 20.45 ± 10.6 kg m^?1 s^?1 MPa^?1 at the base, and increased to 124.73 ± 55.2 kg m^?1 s^?1 MPa^?1 at the crown base. Hydraulic conductivity at the base of the crown was higher than in the base of the trunk due to the high density of vessels in a small cross-section in this height. Furthermore, we found a species-independent relationship between vessel diameter and frequency. We conclude that the differences found in the hydraulic efficiency give some evidence that palms have a lower occurrence of embolism and cavitation than trees, which is due to stiffer and stronger conduit pathways and efficient drought-avoiding strategies. The differences in hydraulic architecture between palms and trees imply different water use patterns thus varying niche differentiation, but this does not consequently need to be an excluding factor for coexistence in the same environment.

     

Effects of vessel-induced waves on the YOY-fish assemblage at two different habitat types in the main stem of a large river (Danube,Austria)

The effects of navigation on young-of-the-year (YOY) fish were investigated for the Danube River based on an integrative approach. During YOY growing season, wave height, wave frequency and water currents were recorded. Synchronously, fish drift and fish abundance of YOY were monitored in two distinct inshore nursery habitats—a gravel bar and a groyne field. The characteristics of vessel-induced waves were correlated to YOY-drift. In both habitats, an increase in drift densities during ship passages was observed. At the same time, assemblage composition and drift densities differed between habitat types. At the gravel bar, drift densities of larval cyprinids—representing many keystone species of the Danube—were higher during ship passages. In the groyne field, drift was low and percids dominated the YOY-assemblage along the shore. Banks with gentle slopes in the main channel seem to be particularly affected by vessel-induced wave wash. Precisely such habitats are often established within the scope of modern river restoration projects because they provide suitable nursery habitats for riverine fish species. Beside the positive effects on biota, the establishment of these habitats in navigable reaches may create problems for YOY-fish due to displacement effects induced by ship-generated waves.     

Fish choruses off Port Hedland,Western Australia

Australian waters are home to a number of vocal species of fish. Cataloguing the acoustic characteristics and temporal patterns of choruses and their locations can provide significant information for long-term monitoring of vocal fishes and their ecosystems. In coastal waters off Port Hedland, Western Australia, two seafloor positioned sea-noise loggers, located 21.5 km apart in 8 and 18 m of water, recorded for an 18-month period. Numerous sound sources were detected, including mooring and vessel noise, humpback whale song and a large variety of fish signal types. Seven fish choruses were identified, occurring predominantly between late spring and early autumn (wet season) and displaying energy from 50 Hz to >4 kHz. Many of these choruses exhibited acoustic characteristics similar to choruses previously reported elsewhere, for some of which the source species or families have been identified. Distinct diurnal patterns in the choruses were observed, associated with sunrise or sunset and in some cases, both. While choruses were predominantly recorded on different days, there were at total of 80 days when more than one chorus was present at the same site. Some pairs of choruses present on the same day exhibited various combinations of temporal and frequency partitioning, while others displayed predominant overlap in both spaces.     

Dispersion and Damping of Gold Surface Plasmon

High-resolution electron energy loss spectroscopy was used to investigate the surface plasmon dispersion in (111)-oriented Au films grown on Cu(111). The measured dispersion of the plasmon mode was positive, as found for Ag. The centroid of the induced charge associated to the plasmon field lies well inside the jellium edge. The damping relation of the Au surface plasmon presented a critical wave vector of 0.11 Å^?1. For higher values of the parallel momentum transfer, the line width of Au surface plasmon considerably increased as a consequence of the opening of a new decay channel via single-particle transitions.     

Effect of hot water treatment on development of anthracnose (Colletotrichum gloeosporioides) and quality of mango fruit at Jimma southwest Ethiopia

Anthracnose is the major postharvest disease of mango and occurs throughout mango producing areas of the world including Ethiopia. Evaluating effect of hot water treatment on development of anthracnose and quality of mango fruit is imperative. A total of three hot water levels 48, 52 and 56 °C at two time interval (5 and 10 min) were tested with factorial arrangement in completely randomised design. The study indicated that hot water treatment at different temperatures and time interval significantly (p < 0.001) affects disease development and shelf life and postharvest quality of mango fruits. Hot water treatments reduced the incidence and severity of anthracnose disease significantly (p < 0.001) in mango fruits as compared to control. There was a highly significant difference (p < 0.0001) on weight loss, total soluble solids, titratable acidity and fruit firmness of mango fruits due to treatment. The present study reviled that hot water treatment has a potential in reducing the postharvest loss due to anthracnose and improving the shelf life and quality of mango fruits. However, the reduction of disease pressure on fruits was not at applicable level, which call ups future effort on developing on integrated disease management strategies for reduction of postharvest loss of mango fruits.     

Extreme water level decline effects sediment distribution and composition in Lake Alexandrina,South Australia

Water level decline affects the biophysical environment of shallow lakes. Unprecedented drought in Australia’s Murray–Darling Basin resulted in extreme water level drawdown in the large, shallow Lake Alexandrina at the end of the River Murray. Surface sediment was collected from 22 sites in the lake before and after water levels declined to assess the integrated limnological changes over the period of drawdown. Results indicate an increase in the proportion of organic particles in profundal sediments, as well as an increase of fine particles (<19.9 μm) in peripheral sediments. These changes to sediment composition corresponded to higher concentrations of suspended particles at low water levels. Increased autochthony and a shift in primary production from macrophytes to phytoplankton in Lake Alexandrina support these findings. Inorganic carbon and other nutrients were lost from sandy sediments most likely through carbonate dissolution driven by a localized decrease in pore water pH from increased mineralisation of organic matter.     

Bicarbonate-based carbon capture and algal production system on ocean with floating inflatable-membrane photobioreactor

This study aims to develop a low-cost microalgae culture system which uses a simple closed vessel as photobioreactor to save manufacturing cost, waves for mixing to save energy cost, and high concentration of bicarbonate for carbon supply to avoid the high cost of CO₂-bubbling pipeline construction on the ocean as well as to control pH by buffering the effect of bicarbonate/carbonate. To test this idea, the alkalihalophilic cyanobacterium Euhalothece sp. was cultured with 1.0 M NaHCO₃ in small-scale floating photobioreactors (PBRs) on 10-cm-high artificial waves at first. The final biomass concentration was up to 0.91 and 1.47 g L^?1 for indoor and outdoor cultures, respectively. However, the recorded dissolved oxygen (DO) was occasionally over-saturated (> 500% of air saturation), indicating mass transfer problem. k _L a in these PBRs with different culture depth was measured then, and the results showed great variation, from 0.13 to 4.87 h^?1. At the scale of 1.0 m², this floating PBR was made with low-cost membrane and inflatable design. It was placed on the ocean surface and mixed with natural waves. Biomass concentration of 1.63 g L^?1 and productivity of 8.27 g m^?2 day^?1 were obtained in this culture. With these results, the feasibility of a low-cost microalgae culture system was proven, which could systematically reduce the cost of photobioreactor manufacturing, operating, and maintenance.