Human Impacts on Wetlands and Mangroves - AP Environmental Science

Which land-use change most increases wetland sedimentation from erosion?
Answer: Clear-cutting a forested watershed upstream, increasing runoff and soil erosion that delivers more suspended sediments to wetlands. Wetland sedimentation increases when upstream land uses accelerate erosion, delivering excess sediments that can smother vegetation and alter hydrology. Clear-cutting forested watersheds removes vegetation, increasing runoff and soil loss, which transports sediments to wetlands. Choice A correctly identifies this as the change most increasing sedimentation. Restoring riparian areas (B), no-till farming (C), silt fences (D), and terracing (E) reduce erosion. Excess sedimentation degrades wetland habitats and reduces water storage capacity. Sustainable land management upstream is key to wetland protection.
After shrimp ponds replace mangroves, storm surge damage rises and fish nursery habitat declines; which impact is most direct?
Answer: Increased coastal erosion and reduced juvenile fish survival because mangrove roots no longer stabilize sediments or provide shelter and food. Mangroves play a crucial role in coastal ecosystems by stabilizing sediments with their intricate root systems, which prevent erosion during storms and high tides. When shrimp ponds replace these mangroves, the loss of roots directly leads to increased coastal erosion as sediments become more susceptible to wave action. Additionally, mangrove forests serve as vital nurseries for juvenile fish, providing shelter and food sources that enhance survival rates. Without this habitat, juvenile fish face higher mortality, leading to declines in overall fish populations. This conversion also exacerbates storm surge damage because mangroves naturally dissipate wave energy, reducing the impact on inland areas. The direct impacts highlight how human alterations disrupt these protective and nurturing functions of mangroves.
A mangrove wetland is used as a landfill; which pollutant risk is most associated with this practice?
Answer: Leachate containing heavy metals and organic contaminants can enter groundwater and estuaries, harming aquatic organisms and humans. Using mangroves as landfills introduces leachate with heavy metals, organics, and nutrients that can contaminate groundwater and nearby estuaries. This pollution harms aquatic organisms through toxicity and bioaccumulation. Human health risks arise from contaminated seafood or water. Landfills disrupt mangrove hydrology and vegetation. Proper siting and liners are needed to prevent such risks. This practice exemplifies poor waste management impacting coastal ecosystems.
Which indicator best suggests a mangrove ecosystem is being stressed by excess freshwater diversion?
Answer: Shift toward freshwater plant species and reduced mangrove seedling survival, indicating salinity regimes are changing beyond tolerance. Mangroves thrive in brackish environments where salinity is balanced by tidal and freshwater inputs, supporting specialized adaptations like salt excretion. Excess freshwater diversion reduces salinity, stressing mangroves and favoring freshwater-tolerant plants, which can outcompete mangrove seedlings and alter community composition. Choice A correctly identifies this shift and reduced seedling survival as key indicators of stress. Increased coral cover (B) is unlikely in shaded, sediment-rich mangrove areas. Higher tidal amplitude (C), increased height (D), and lower oxygen in trunks (E) are not direct effects of freshwater excess. This stress can lead to mangrove die-off, reducing coastal protection and fisheries habitat. Monitoring such indicators helps in managing diversions to maintain ecosystem balance.
Mangrove clearing increases water temperature in lagoons; which consequence is most likely for dissolved oxygen?
Answer: Dissolved oxygen decreases because gas solubility declines with temperature, increasing hypoxia risk especially at night. Mangroves shade coastal lagoons, moderating water temperatures and supporting dissolved oxygen levels essential for aquatic life. Clearing mangroves allows more sunlight, warming the water, and since warmer water holds less dissolved oxygen, this increases hypoxia risks, especially at night when photosynthesis ceases. Choice B correctly explains this decrease in oxygen solubility and hypoxia threat. Increased oxygen (A and E) contradicts gas solubility principles. Constant oxygen (C) ignores temperature's role. Negative oxygen (D) is impossible. These changes can lead to fish kills and reduced biodiversity in lagoons, highlighting mangroves' role in maintaining water quality.
A mangrove forest is degraded by boat propeller scars; which recovery factor is most limiting?
Answer: Recolonization by mangrove seedlings may be limited by altered hydrology and unstable sediments in scars, slowing natural recovery. Mangrove forests recover from disturbances like propeller scars through seedling recolonization, but altered hydrology and unstable sediments in scars can limit establishment by causing erosion or improper inundation. Choice A accurately notes these limiting factors. Temperature alone (B), inability to regrow (C), increased nutrients (D), and deepening scars (E) do not correctly explain limitations. Scars reduce habitat complexity and productivity. Active restoration, like stabilizing sediments, can aid recovery. Protecting mangroves from boating damage preserves their ecological roles.
A coastal wetland is converted to a parking lot; which change in hydrograph is most likely?
Answer: Higher peak discharge and shorter lag time because impervious cover increases runoff volume and speed during storms. Converting wetlands to parking lots increases impervious surfaces, which prevent infiltration and accelerate runoff during storms. This leads to higher peak discharges in streams, as water reaches them faster and in greater volumes. Shorter lag times between rainfall and peak flow increase flood risks. Baseflow may decrease due to reduced groundwater recharge. Such changes alter stream ecosystems, potentially causing erosion and habitat loss. The hydrograph shift illustrates urbanization's impact on hydrology.
A wetland is isolated by levees; which ecological effect is most likely?
Answer: Reduced nutrient exchange and altered hydroperiod, decreasing productivity and disrupting life cycles of fish and amphibians. Wetlands rely on hydrological connectivity with rivers and tides for nutrient exchange, sediment delivery, and species migration, which sustain productivity and biodiversity. Levees isolate wetlands, disrupting the hydroperiod (flooding patterns) and reducing nutrient inputs, which can lower plant growth and affect species like fish and amphibians that depend on seasonal flooding. Choice A accurately captures these effects on productivity and life cycles. Increased connectivity (B) is the opposite of isolation. Higher sediment deposition (C) may occur with levees but not from concentrated floods in isolated systems. No effect (D) ignores wetlands' open nature, and invasive elimination (E) overlooks dispersal methods. Isolation degrades overall ecosystem health and services like flood attenuation.
A wetland is contaminated with mercury; which statement best describes a human health concern?
Answer: Mercury can bioaccumulate and biomagnify in aquatic food webs, increasing concentrations in predatory fish consumed by humans. Mercury in wetlands can methylate into toxic forms that bioaccumulate in organisms and biomagnify up food chains, posing health risks to humans consuming contaminated fish. Choice A accurately describes this concern. Harmless conversion (B), air-only exposure (C), decreasing biomagnification (D), and plant-only effects (E) are incorrect. This highlights wetlands' role in contaminant cycling. Monitoring and reducing mercury inputs protect public health. Advisories on fish consumption mitigate risks.
A wetland is filled, reducing local bird populations; which explanation best links habitat loss to biodiversity decline?
Answer: Wetlands provide feeding and nesting sites; filling reduces carrying capacity, causing population declines and local extirpations. Wetlands are critical habitats for birds, offering feeding grounds, nesting sites, and protection from predators due to their complex vegetation and water features. Filling a wetland directly reduces the available area for these activities, lowering the carrying capacity for bird populations. This habitat loss can lead to declines in abundance and diversity, with some species facing local extirpation if alternative sites are unavailable. Specialist birds that rely on wetland conditions are particularly affected, as filled areas often become unsuitable for their needs. The link between habitat destruction and biodiversity decline emphasizes the importance of preserving wetlands for avian conservation. Overall, such actions disrupt food webs and ecological balances in the region.
Which human impact most directly reduces wetland groundwater recharge capacity?
Answer: Soil compaction and increased impervious surfaces, which reduce infiltration and alter natural water storage and movement. Urbanization compacts soils and adds impervious surfaces, decreasing infiltration and disrupting groundwater recharge in wetlands. Choice A directly reduces recharge capacity. Planting natives (B), removing invasives (C), adding debris (D), and increasing beavers (E) generally enhance infiltration. This impact alters hydrology and ecosystem stability. Low-impact development preserves recharge. Wetlands are vital for aquifer sustainability.
A wetland receives untreated sewage; which parameter most directly signals organic pollution loading?
Answer: High biological oxygen demand (BOD), because microbial decomposition of organic matter consumes dissolved oxygen in the water. Untreated sewage introduces high levels of organic matter into wetlands, which microbes decompose, consuming dissolved oxygen and raising biological oxygen demand (BOD). Elevated BOD is a key indicator of organic pollution, leading to hypoxic conditions that stress aquatic life. Wetlands can naturally process some organic loads through filtration and microbial activity, but overloads degrade water quality. Monitoring BOD helps assess pollution impacts and the need for treatment. This parameter directly links human waste inputs to ecosystem health declines. Overall, it underscores the importance of wastewater management to protect wetlands.
A city drains a freshwater marsh for housing; which ecosystem service is most immediately lost?
Answer: Floodwater storage and peak-flow reduction because wetlands temporarily hold stormwater and slow its movement downstream. Freshwater marshes act as natural sponges, absorbing and storing floodwaters during heavy rainfall, which helps mitigate downstream flooding. When a marsh is drained for housing, this floodwater storage capacity is lost, leading to increased peak flows in nearby streams and rivers. The ecosystem service of peak-flow reduction is immediately compromised, as the wetland no longer slows the movement of stormwater. This can result in more frequent and severe flooding in urban areas, affecting human infrastructure and safety. Additionally, marshes support biodiversity by providing habitats for various species, but the primary immediate loss here is hydrological regulation. Overall, such development underscores the importance of wetlands in managing water cycles and preventing flood-related damages.
A drained peat wetland is converted to agriculture; which greenhouse gas effect is most likely?
Answer: Higher CO $_2$ emissions because drainage introduces oxygen, accelerating decomposition of stored peat carbon into the atmosphere. Peat wetlands store large amounts of carbon in waterlogged, anaerobic soils where decomposition is slow. Draining these wetlands introduces oxygen, accelerating microbial decomposition of organic matter and releasing stored carbon as CO2 into the atmosphere. This process contributes to higher greenhouse gas emissions, exacerbating climate change. Agriculture on drained peat can further disturb soils, amplifying emissions. Methane production may decrease due to less anaerobic conditions, but CO2 release dominates the impact. Understanding this highlights the role of intact wetlands in carbon sequestration and the risks of conversion.
A wetland is invaded by an aggressive nonnative plant after disturbance; which mechanism best explains invasion success?
Answer: Disturbance reduces native competitors and creates open niches; invaders exploit resources quickly and can outcompete natives. Disturbance in wetlands creates open niches by reducing native plant cover and altering conditions, favoring fast-growing invasive species. Invaders often have traits like rapid reproduction that allow them to outcompete natives for resources. This can lead to monocultures, reducing biodiversity and altering ecosystem functions. Native competitors are weakened, facilitating invasion. Restoration focuses on minimizing disturbances and removing invasives. The mechanism explains many successful invasions in altered habitats.
Road construction fragments a mangrove forest; which outcome is most likely for edge areas?
Answer: Greater exposure and altered salinity, increasing stress and invasion risk compared with interior mangrove habitat. Fragmentation of mangrove forests by roads creates edge habitats that are more exposed to environmental stressors like wind, light, and salinity fluctuations. These edges experience greater stress, making them susceptible to invasion by non-native species that thrive in disturbed conditions. Interior mangroves, by contrast, maintain more stable conditions favorable to native species. Fragmentation can also reduce genetic diversity and population viability due to isolation. Edge effects often lead to decreased productivity and altered community structures in mangroves. This outcome demonstrates how human infrastructure can indirectly degrade coastal ecosystems through habitat fragmentation.
A wetland is restored but invasive cattails dominate; which outcome is most likely for habitat quality?
Answer: Lower habitat heterogeneity and reduced native species diversity because monocultures can simplify structure and alter food webs. Invasive cattails can form monocultures in restored wetlands, reducing habitat heterogeneity and displacing native species, which lowers biodiversity and alters food webs. Choice A correctly predicts lower habitat quality. Guaranteed biodiversity increase (B), nutrient elimination (C), higher salinity (D), and no change (E) are unlikely. Invasives disrupt ecosystem functions. Control measures are essential for successful restoration. Diverse native communities enhance resilience.
A mangrove area is converted to salt pans; which biodiversity outcome is most likely?
Answer: Decreased biodiversity because habitat complexity and nursery areas are lost, and extreme salinity excludes many organisms. Mangroves provide complex habitats with roots that serve as nurseries for fish and shelter for birds, supporting high biodiversity. Converting to salt pans simplifies the habitat into hypersaline ponds, excluding many species adapted to mangrove conditions and reducing overall diversity. Choice B correctly identifies decreased biodiversity due to lost complexity and salinity extremes. Increased richness (A), no change (C), coral increase (D), and mammal diversity (E) are unlikely outcomes. This conversion diminishes ecosystem services like fisheries and coastal protection. Restoration efforts are needed to recover lost biodiversity.
A mangrove forest is replaced by rice paddies; which carbon-cycle change is most likely?
Answer: Increased greenhouse gas emissions because lost biomass and disturbed soils release stored carbon, and paddies can emit methane. Replacing mangroves with rice paddies removes carbon-storing biomass and disturbs soils, releasing CO2 from decomposition. Flooded paddies promote anaerobic conditions, increasing methane emissions from methanogenic bacteria. This net increase in greenhouse gases contributes to climate change. Mangroves sequester carbon more effectively long-term. Sustainable land use should avoid such conversions. The change disrupts global carbon cycles linked to coastal ecosystems.
A mangrove shoreline is replaced by a sandy beach nourishment project; which trade-off is most accurate?
Answer: Beach recreation may increase, but loss of mangrove habitat reduces nursery areas and natural shoreline stabilization services. Replacing mangroves with sandy beaches may boost recreation but sacrifices nursery habitats, fisheries support, and natural stabilization, increasing erosion risks. Choice A accurately describes this trade-off. Biodiversity increase (B), permanent erosion elimination (C), reduced turbidity (D), and no trade-off (E) are incorrect. Nourishment projects should consider ecological impacts. Integrated management balances human and ecosystem needs. Long-term costs of habitat loss can outweigh short-term gains.

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