📚 Year 8 SQA Science: Case Study in Action | 八年级 SQA 科学：案例分析实战演练
Welcome to this case study practical exercise designed for Year 8 SQA Science. In this activity, you will step into the role of an environmental scientist investigating the health of a freshwater loch. You will analyse real data, identify patterns, and draw evidence-based conclusions — just like scientists do in the field.
欢迎参加为八年级 SQA 科学设计的案例分析实战演练。在这个活动中，你将扮演环境科学家，调查一个淡水湖泊的健康状况。你将分析真实数据，识别规律，并得出基于证据的结论——就像科学家在实地所做的那样。
1. Introduction to the Case Study | 案例介绍
A local community has reported a decline in fish populations in Muirburn Loch over the past two years. As part of a scientific team, you must investigate whether water quality has changed and what might be causing the problem. Your tools are data tables, graphs, and your understanding of scientific inquiry.
当地社区报告，过去两年穆尔本湖的鱼类数量有所下降。作为科学团队的一员，你必须调查水质是否发生了变化，以及可能的原因是什么。你的工具是数据表格、图表，以及你对科学探究的理解。
2. Background: Muirburn Loch | 背景：穆尔本湖
Muirburn Loch is a shallow freshwater loch in Scotland, surrounded by farmland and a small village. Runoff from fertilisers and occasional sewage leaks can affect the water. Healthy freshwater ecosystems typically have a pH between 6.5 and 8.5, dissolved oxygen above 5 mg/L, and water temperatures between 5°C and 20°C depending on the season.
穆尔本湖是苏格兰的一个浅水淡水湖，周围有农田和一个小村庄。化肥径流和偶尔的污水泄漏可能影响水质。健康的淡水生态系统通常 pH 值在 6.5 至 8.5 之间，溶解氧高于 5 毫克/升，水温根据季节在 5°C 至 20°C 之间。
You will examine data collected over six months from three sampling sites: Site A (near the village), Site B (mid-loch), and Site C (near farmland). To make the analysis manageable, we will focus on three representative months: January, March and May.
你将检查从三个采样点在六个月期间收集的数据：A 点（靠近村庄）、B 点（湖中央）和 C 点（靠近农田）。为了使分析易于处理，我们将集中研究三个有代表性的月份：一月、三月和五月。
3. Data Collection Methods | 数据收集方法
Scientists measured water temperature using a digital thermometer, pH using a calibrated pH meter, and dissolved oxygen using a chemical test kit (the Winkler method). Samples were taken once a month at the same time of day to ensure a fair test. Control variables included sampling depth and the fact that all measurements were taken by the same person using the same calibrated equipment.
科学家使用数字温度计测量水温，使用校准后的 pH 计测量 pH 值，并使用化学测试套件（温克勒法）测量溶解氧。每月在一天中的同一时间采集样本，以确保公平测试。控制变量包括采样深度，以及所有测量均由同一个人使用相同的校准设备进行。
They also recorded the number of fish species observed during a 30-minute visual survey from a boat, always at 10:00 am to reduce variation.
他们还记录了在上午 10:00 从船上进行 30 分钟目测调查时观察到的鱼类物种数量，以减少差异。
4. Table of Results | 结果数据表
The table below shows the data collected at each site during the three selected months. Study the numbers carefully and look for trends. Notice how temperature rises in May for all sites, but the other measurements change differently depending on the site.
下表显示了在三个选定月份从每个地点收集的数据。仔细研究这些数字，并寻找趋势。注意五月份所有地点的温度都上升了，但其他测量值的变化因地点而异。
| Site | Month | Temperature (°C) | pH | Dissolved Oxygen (mg/L) | Number of Fish Species |
|---|---|---|---|---|---|
| A (Village) | Jan | 4 | 7.8 | 8.0 | 8 |
| A (Village) | Mar | 6 | 7.6 | 7.5 | 7 |
| A (Village) | May | 12 | 7.2 | 7.0 | 6 |
| B (Mid-loch) | Jan | 4 | 7.9 | 8.2 | 10 |
| B (Mid-loch) | Mar | 6 | 7.8 | 8.0 | 9 |
| B (Mid-loch) | May | 12 | 7.7 | 7.8 | 8 |
| C (Farmland) | Jan | 4 | 8.2 | 8.0 | 9 |
| C (Farmland) | Mar | 6 | 8.5 | 7.2 | 7 |
| C (Farmland) | May | 12 | 8.9 | 6.5 | 5 |
5. Calculating Mean Values | 计算平均值
To get an overall picture of water quality, scientists often calculate the mean for each site. The mean helps smooth out small variations and reveals the central tendency. Let us calculate some key means using the data from all three months.
为了全面了解水质，科学家通常会计算每个地点的平均值。平均值有助于平滑微小的变化并揭示集中趋势。让我们使用所有三个月的数据计算一些关键的平均值。
Mean pH at Site C = (8.2 + 8.5 + 8.9) ÷ 3 = 25.6 ÷ 3 ≈ 8.53. This is already above the upper limit of the healthy pH range (8.5), suggesting a possible pollution problem.
C 点的平均 pH = (8.2 + 8.5 + 8.9) ÷ 3 = 25.6 ÷ 3 ≈ 8.53。这已经超过了健康 pH 范围的上限（8.5），表明可能存在污染问题。
Mean dissolved oxygen at Site C = (8.0 + 7.2 + 6.5) ÷ 3 = 21.7 ÷ 3 ≈ 7.23 mg/L. Although still above 5 mg/L, the downward trend is worrying.
C 点的平均溶解氧 = (8.0 + 7.2 + 6.5) ÷ 3 = 21.7 ÷ 3 ≈ 7.23 mg/L。虽然仍高于 5 mg/L，但下降趋势令人担忧。
Now try these yourself: (i) Mean fish species at Site B; (ii) Mean dissolved oxygen at Site A. (Answers: B mean fish = 9; A mean DO = 7.5 mg/L). These calculations help you quantify changes and compare sites objectively.
现在请你自己尝试：(i) B 点的平均鱼种数；(ii) A 点的平均溶解氧。（答案：B 点平均鱼种 = 9；A 点平均 DO = 7.5 mg/L）。这些计算帮助你量化变化并客观地比较各地点。
6. Identifying Variables | 识别变量
In this investigation, what was the independent variable? The independent variable is the factor that was deliberately changed or compared — in this case, the sampling location (Site A, B or C). The dependent variable is what was measured as a result: each water quality parameter (pH, dissolved oxygen, fish species count).
在这个调查中，自变量是什么？自变量是故意改变或进行比较的因素——在这个案例中，是采样地点（A、B 或 C 点）。因变量是因此测量的结果：每一个水质参数（pH、溶解氧、鱼类物种计数）。
Several variables were controlled to make the investigation a fair test: sampling time (same day each month, same hour), sampling depth, measurement instruments (all calibrated), and the person collecting the data. Controlling these meant that any differences observed were likely due to the site, not other factors.
有几个变量被控制以使调查成为一个公平的测试：采样时间（每月同一天，同一小时）、采样深度、测量仪器（均经校准）以及收集数据的人。控制这些意味着观察到的任何差异很可能都是由地点引起的，而不是其他因素。
7. Drawing a Bar Chart | 绘制条形图
Create a bar chart comparing the mean number of fish species at each site over the three months. Use the mean values: Site A = (8+7+6) ÷ 3 = 7; Site B = (10+9+8) ÷ 3 = 9; Site C = (9+7+5) ÷ 3 = 7.
制作一张条形图，比较三个月期间每个地点的平均鱼类物种数量。使用的平均值：A 点 = 7；B 点 = 9；C 点 = 7。
On your chart, label the x-axis ‘Sampling Site’ and the y-axis ‘Mean Number of Fish Species’. Draw evenly spaced bars of equal width, and give your chart a clear title such as ‘Average fish species count at three sites in Muirburn Loch’.
在你的图表上，将 x 轴标注为“采样地点”，y 轴标注为“平均鱼类物种数”。绘制间距均匀、宽度相等的条形，并给图表一个清晰的标题，例如“穆尔本湖三个地点平均鱼类物种数”。
Looking at the chart, Site B stands out as the most biodiverse site. Although Sites A and C have the same average, Site C showed a steep decline from 9 to 5 species, which is masked by the mean. This is why we must also look at trends over time, not just averages.
从图表上看，B 点生物多样性最突出。尽管 A 点和 C 点的平均值相同，但 C 点显示出从 9 种急剧下降到 5 种，这一情况被平均值掩盖了。这就是为什么我们还必须观察随时间变化的趋势，而不仅仅是平均值。
8. Interpreting the Data | 解读数据
The pH at Site C rose from 8.2 to 8.9 over the months, while dissolved oxygen dropped from 8.0 to 6.5 mg/L. What could explain this pattern? A rise in pH often occurs when algae grow rapidly due to excess nutrients (a process called eutrophication). During the day, algae photosynthesise, consuming carbon dioxide and raising the pH. However, when algae die and decompose, bacteria use up oxygen, causing dissolved oxygen levels to fall.
C 点的 pH 值从 8.2 上升到 8.9，而溶解氧从 8.0 下降到 6.5 mg/L。什么可以解释这种模式？当藻类因营养过剩而快速生长（这一过程称为富营养化）时，pH 值常常上升。白天，藻类进行光合作用，消耗二氧化碳，使 pH 值升高。然而，当藻类死亡并被分解时，细菌消耗氧气，导致溶解氧水平下降。
Site A also showed a decline in oxygen (8.0 to 7.0 mg/L) and fish species (8 to 6), possibly due to nutrient input from the village. Site B remained relatively stable, with pH staying within the healthy range and dissolved oxygen dropping only slightly. This suggests that the mid-loch area is less affected by runoff.
A 点也显示出氧气（8.0 到 7.0 mg/L）和鱼种数（8 到 6）的下降，可能是由于村庄输入的营养物。B 点保持相对稳定，pH 值保持在健康范围内，溶解氧仅略有下降。这表明湖中央区域受径流的影响较小。
Overall, there is a negative correlation between pH and dissolved oxygen at the affected sites, and a positive correlation between dissolved oxygen and the number of fish species. High nutrient levels appear to trigger the chain of events.
总体而言，在受影响的地点，pH 值与溶解氧之间存在负相关，溶解氧与鱼类物种数之间存在正相关。高营养水平似乎引发了一系列事件。
9. Drawing Conclusions | 得出结论
Based on the data, what can you conclude about the health of Muirburn Loch? The evidence strongly suggests that nutrient pollution is affecting the loch. Site C, near farmland, is the most impacted, with rising pH and falling oxygen levels leading to a sharp decline in fish species. Site A also shows signs of stress, likely from village runoff.
根据数据，关于
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